recovery intervals PHA
Polarised training Intensityfartlek speed MHR INTERVAL EDT TRAINING HIT YOUR ULTIMATE FITNESS AND SPORT PERFORMANCE TOOL ACT sprints
TabataAndrew Hamilton power flexibility workouts lactate threshold VO2max
INTERVAL TRAINING YOUR ULTIMATE FITNESS AND SPORT PERFORMANCE TOOL
INTERVAL TRAINING YOUR ULTIMATE FITNESS AND SPORT PERFORMANCE TOOL
© Green Star Media Ltd 2016 Published by Green Star Media Ltd Meadow View, Tannery Lane, Bramley, Guildford, Surrey, GU5 0AB. United Kingdom.
Publisher: Jonathan A. Pye Editor: Andrew Hamilton
The information contained in this publication is believed to be correct at the time of going to press. Whilst care has been taken to ensure that the information is accurate, the publisher can accept no responsibility for the consequences of actions based on the advice contained herein.
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without the permission of the publisher. coNTENTs
An introduction to and history of interval training 1
Why does interval training work? 5
Anatomy of interval training 11
Rest and recovery 20
High intensity interval: why less can be more! 28
Intervals: good for health as well as performance! 37
Intervals: looking at the bigger picture 43
Interval Training Workouts 52
interval training for endurance 52
interval training and sports performance 55
interval training for speed 58
interval training for fitness 61
interval training and resistance training 64
Some frequently asked questions about interval training 69
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An introduction to and history of interval training
What is interval training and how did it evolve to become such an effective form of training?
Introduction Distilled down to the very basics, ‘interval training’ is a method of training that intersperses intervals of high-intensity exercise, with short periods of rest. Why has this type of training become so popular among elite sportsmen and women? The answer, dear reader, is easy – done right, interval training allows you to get bigger fitness gains, faster than simply ploughing along endlessly at a steady intensity (we’ll explore why this is in the next chapter).
But if interval training is so effective, why doesn’t everybody do it? Well, mention intervals to anyone that has participated in organised sport and the chances are you’ll open a floodgate of (mostly unpleasant) memories of gruelling and monotonous efforts on the field or track, in the pool, on the pitch etc! And that’s a big shame because interval training doesn’t have to be like that. As we’ll see in the coming chapters, recent findings from the world of sports science show that interval training can be quicker and easier than most people imagine. Better still, it’s also becoming clear that interval training can benefit everybody and anybody who exercises or participates in sport, whatever the level – not just in terms of sport performance but also by providing significant health benefits. In short, whether you exercise for fitness or train for sport, if you don’t include intervals in your programme, you’re losing out.
Interval training: history and background It’s hard to say exactly where, when and how interval training first emerged as a training tool. We know that just over 100 years ago, the Finnish runner Paavo Nurmi and his coach Lauri Pikhala put together a system of training that includes what we might call intervals today. Also, the Finnish gold medallist (5k, 10k, 8k, and cross-country) Hannes Kolehmainen prepared for his Olympic performances by using a type of interval training. Both of these runners focused on alternating fast and slow runs and in some cases they would ramp up the effort, while decreasing the distance.
However, it was a little later before modern interval training began to properly emerge. The history books recount how Germany in the 1930s was a nation
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preparing for a war that was to engulf the planet. However, two physiologists named Reindell and Gerschler had other matters on their mind. They had been studying the various functions of the human body and applying their findings to athletic performance. With the aid of a physician, Reindell and Gerschler tried to develop a method to train the heart muscle in the same way that other muscles would be trained. They found that repeated runs of 100-200 metres proved to be very effective and they had great success with one runner, Rudolf Harbig, who went on to set the world record for 400 metres. This was a golden age of sport science where the best physiologists in the world and best track coaches were working simultaneously. It resulted in the development of the now widely accepted ‘heart rate zones’ during exercise and the exact rest periods for the heart to return to a particular level before the next bout of intervals.
During the years that followed, another German physiologist called Franz Stampfl moved from Germany to England and brought the interval training idea with him. His idea was different: some runners who can’t run a mile in 4 minutes can still run two miles at the same pace, if those two miles are divided into 8 x quarter miles with short rests in between. In other words, splitting the race distance into smaller segments and running these at the required race pace allows runners to do far more work at race pace than if they attempted the distance in one continuous hit.
Stampfl’s idea caught the attention of a medical student called Roger Bannister, who used his medical background and Stampfl’s method to break the 4-minute barrier for the mile! Interestingly, when Bannister wrote about his training methods in a subsequent book, he only mentioned the last 10 workouts he did. This caused much confusion and endless troubles for those who tried to emulate his success because Bannister failed to mention that he was tapering (reducing his training volume and intensity) during these workouts! However, the importance of Bannister’s approach cannot be underestimated; apart from breaking through what seemed to be an unbreakable barrier, running a 60-second 400 metres ten times, with a rest of two to three minutes in between each effort, is still the starting point for those wishing to run a mile in less than four minutes!
Beyond the mile Training at race pace, in short, produced great results for Bannister over the mile distance. But it soon became apparent that it was restricted in its application for significantly longer events – certainly beyond 5km. The next step in the evolution of interval training came in the late 40s and 50s when Czech runner Emil Zatopek
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(and others) realised that there was a limit to Bannister’s approach. For example, in no way would 12 x intervals of 3 miles be appropriate for marathon training! Instead, the idea was to perform an interval workout and then build upon it, either by increasing the number of repetitions, increasing the pace, lengthening each repeat or decreasing the time interval in between reps. This led to a bewildering array of different interval workouts, each with its own benefits and drawbacks. However, the proof of the pudding was in the eating because at the 1952 Summer Olympics in Helsinki, Zátopek won gold in the 5km, 10 km, and the marathon. He also broke the existing Olympic record in each of the three events!
Fast forward to the late 60s and early 70s, and interval training took another step forward. This was because there were enough runners doing enough different workouts to compare them, which allowed sports scientists and coaches to use actual empirical evidence to determine what worked best and what didn’t. In California, Gerry Purdy and Jim Gardner were computer scientists and running fanatics who began hypothesising about the relationship between a runner’s level of ability and the workouts he or she could perform. They turned it into a science project and developed a scoring system that could pinpoint the fitness of any runner. They then published their results in 1970 in ‘Computerized Running Training Programs’, which soon became a bible for thousands of track coaches and runners.
The essence of Purdy and Gardener’s finding was that runners could only run at 95% effort once, but could run at 90% two or three times with a 4-5 minute rest, 85% four or five times with a 3-4 minute rest, 80% six to nine times with a 2-3 minute rest, 75% ten to fifteen times with a 90-120 second rest and 70% up to 30 times with a 60-90 second rest and at any distance. This allowed coaches to write workouts quickly for several members of a team at once and before long, every college and school had a copy. Unfortunately, however, it also taught a whole generation of athletes to hate intervals!
Modern interval training Interval training has remained popular since the late 60s, albeit with some resistance from coaches down under – for example, Percy Cerutty in Australia and Arthur Lydiard in New Zealand. Cerutty was known to dislike interval training and his training philosophy added resistance training to running – for example, his runners often ran on beaches and up and down dunes or ran with weights. Meanwhile, Lydiard developed an approach that emphasised very high training volumes with little interval content. While this approach is now eschewed by most coaches and sports physiologists, Lydiard did go on to develop
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the (now essential) tool of ‘periodisation’, which ensured his high-mileage runners were able to recover by drastically reducing their training mileage at certain times of the year, and also to peak for specific events.
In more recent years, other athletes, particularly those engaged in sports requiring power/speed as well as endurance (eg soccer, football, basketball, hockey, tennis, swimming, cycling etc), have adopted interval training as a key technique for improving cardiovascular endurance. Intervals have proven to be a better method of training these athletes because high volumes of long-distance training at 70- 80% of maximum heart rate can be detrimental to strength and power. Intervals on the other hand allow these athletes to vary the duration and intensity of the work period and the duration of rest periods to meet the power/speed needs of their particular sport while continuing to develop cardiovascular (aerobic) fitness.
Moving right up to date, interval training is still as popular as ever as part of an overall training programme (good as they are, intervals are not a magic formula or universal solution!). One important development however is that of high- intensity interval training. In 1996, Izumi Tabata of the National Institute of Fitness and Sports in Kanoya, Japan published the results of his study on the effects of high-intensity interval training. He showed that just 8 intervals of 20 seconds of work interspersed with 10 seconds of rest produced excellent gains in fitness. In particular, he demonstrated that high-intensity intervals: l achieved very substantial gains in aerobic capacity (cardiovascular fitness); ●●produced anaerobic (speed/power) benefits for athletes that could not be achieved with steady state aerobic exercise alone; ●●required less time to produce the equivalent gains observed in other types of interval training; The interest in high-intensity interval training has remained and Tabat’s findings have been supported in a number of other studies across a wide range of sports. Another potential benefit of high-intensity interval training is that many athletes (especially non-elite sportsmen and women) anecdotally report that they are less onerous to perform, which makes them attractive for those who can’t or won’t contemplate very tough workouts! Given the importance of this topic, high-intensity interval training is given its own chapter later on in this report.
Summary Coaches, athletes, and scientists will continue to study and experiment with interval training but in the meantime, the history of intervals tells us that they are an extremely versatile conditioning method that you can and should incorporate into your training, whatever your fitness level!
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Why does interval training work?
As we saw in the preceding chapter, interval training is a supremely efficient way of maximising your fitness and sport performance. But why are intervals so effective and how do they work to improve the fitness those who perform them?
Whatever your sport, it’s a fact that grinding out steady state, one-pace workouts will only really produce performance gains in the earlier stages of training. In these early stages, merely commencing an exercise programme at a steady pace provides the muscles and cardiovascular (heart, lung, circulation) system with enough of a stimulus to produce a ‘training adaptation’ (an increase in fitness that occurs as a result of a period of training). However, once your muscles and cardiovascular system have adapted to this steady- state routine, you will reach the performance plateau that one-paced training inevitably brings. Therefore, in order to produce further gains in aerobic capacity and power, you need to further challenge the muscles and energy systems in your body by working them harder.
At this point, you have a number of options, one of which is to simply up your basic steady-state training pace. To an extent, this can work but there’s a big downside; a significant increase in pace sustained across all of your workouts would place a lot of stress on your body, leaving you both exhausted and injury-prone.
Another option would be to keep to the same pace but steadily increase your training volume, for example by running/swimming/rowing/cycling etc further and further in some or all of your workouts. Again, this can work to an extent (this was the approach preferred by the New Zealand coach Lydiard) because high volumes of training can further improve the efficiency of the circulatory system (transporting blood and oxygen to your working muscles) and the efficiency of the muscles in using oxygen to produce energy, especially from fat.
There are two downsides, however: the first is that higher volumes of training, even at low intensity, dramatically increase injury risk; the second is that while this approach is great for helping to develop your ability to run/swim/row/cycle etc for longer, it does little to help you perform these activities any faster, which after all is what most people want. If you want to increase your basic speed, you need to include some training elements that acclimatise the muscles to
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performing at higher speeds. The third drawback, of course, is time. Even the busiest people can squeeze in an hour’s worth of training here and there but two or three-hour workouts are another matter!
It’s for all these reasons that coaches use other training strategies (see box 1), which still place an increased demand on the body’s energy systems but, importantly, do it for relatively short periods of time only so as not to overwhelm the body’s capacity to adapt.
Box 1: Popular strategies to help increase endurance performance
●●Interval training –usually consisting of between 4-8 periods of fairly intense work, interspersed with periods of rest or active recovery. Interval sessions are very flexible; you can vary the number of intervals performed, the length of these intervals, the interval intensity and the length of the rests between the intervals to create an almost unlimited number of permutations (discussed at length in the next chapter).
●●Fartlek training –‘fartlek’ comes from the Swedish language and literally means ‘speed play’. Fartlek is a looser, less punishing form of interval training, which can inject intensity and variety into an otherwise steady state workout. The main objective is to let your body decide how and when to perform harder bursts so for example, during a workout, you up your tempo for a short while and then recover without timing yourself, only going again when you feel ready for it.
●●Fast/race-paced training – consists of a much shorter but significantly faster paced session, which places increased demands on your aerobic system and helps improve your muscle ability to delay the onset of lactate accumulation (see box 1).
Given that there are a number of options for enhancing endurance performance available to athletes and coaches, the obvious question is which strategy will work best? At the top of the list must be interval training. First described by German researchers Reindell and Roskamm, interval training was popularised in the 1950s by the Olympic champion, Emil Zatopek. More importantly, there’s excellent empirical evidence that a wide variety of interval training protocols are effective for enhancing the efficiency of the different energy producing systems in the muscles(1) (see box 2), and this helps to explain why intervals are now used so widely.
Targeting energy systems The flexible structure of intervals (duration and intensity of each interval, rest
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period etc) also means that different sessions can be targeted at the different energy systems required for an athlete’s particular event. For example, 100m sprinting relies heavily on the phosphocreatine system, so would use very short but intense intervals. By contrast, 800m running relies heavily on the lactate system, so, in theory at least, would benefit from intervals that target this system.
Box 2: Energy systems in the body
When you train, your supply of energy throughout the source of a workout appears to be seamless. However, there are actually 4 different energy systems in the body, which work together to ensure that your energy needs in a wide array of circumstances can be met. These energy systems are:
1. The ATP system – this relies on the breakdown of a high-energy molecule called ATP (adenosine triphosphate) within the muscles. The ATP system supplies immediate energy for first 1-4 seconds, but is very soon exhausted;
2. The Phosphocreatine (PC) system – this energy system helps bolster flagging ATP stores very rapidly by regenerating broken down ATP. It does this by transferring high-energy phosphate from stored muscle creatine phosphate to the expended ATP, which regenerates high- energy ATP again. The CP system provides about 10 seconds’ worth of energy and this is the energy system that is bolstered when supplemental creatine is taken;
3. The lactate system – this system helps to regenerate ATP fairly rapidly by the incomplete breakdown of carbohydrate – ie when there’s not enough oxygen available for aerobic energy production (below). The lactate system can supply about a minute’s worth of ATP. However, there is a price to pay because when this system becomes dominant, blood levels of lactate begin to accumulate, causing that familiar ‘burning fatigue’ sensation in muscles;
4. Aerobic system – this system provides by far the bulk of our energy requirements by combining fat, carbohydrate and even protein with oxygen to produce ATP, albeit more slowly. Providing there’s enough oxygen available to the working muscles, the aerobic system can provide energy for several hours!
Biochemistry of intervals Okay, we know that intervals are very flexible so can be used to target various energy systems and we also know that they’re very effective. What’s less well understood, however, is why they’re so effective. Studies have shown that per unit of time invested, intervals are far more effective at producing physiological adaptations leading to fitness and performance gains than steady state
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Box 3: Relative contributions of energy systems during maximal exercise
100
Aer=glycolytic ATP-PC
Aer=lipolytic An-glycolytic Contibution of total work (%)
0.1 1 10 100 1000 Duration of exercise (min)
Key: * The red line represents the combined energy supply of the ATP and PC systems * The green line represents contribution from the lactate system * The white and blue lines represent the contribution of the aerobic system to energy demands from carbohydrate and fat burning respectively
endurance exercise. For example, a 2006 study demonstrated that 2.5 hours of sprint interval training produced similar biochemical muscle changes to 10.5 hours of endurance training and similar endurance performance benefits(2). There’s also evidence that interval training (especially when the intervals are fairly intense) increases your resting metabolic rate – ie the rate at which you burn calories while at rest – for the following 24 hours after training, and that it can also improve your maximal oxygen consumption (VO2 max) more effectively than doing only traditional, steady-state long aerobic workouts(3-6).
But why should this be the case? What adaptation is interval training very good at stimulating in the muscles that traditional steady-state training isn’t so good at? A very simple answer would be that because the high-intensity work is broken down into bite-sized chunks in interval training, you can accumulate far more time overall performing high-intensity exercise than if you tried to maintain that same pace continuously. So, for example, if you were to perform 8 x 30-second intervals at 95% of your maximum power, you would probably find this hard, but
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perfectly manageable. By contrast, trying to maintain 95% of maximum power for 4 minutes would be impossible; even if you got halfway there, the chances are you’d feel very ill indeed and would have to abandon the workout!
Delving deeper To properly understand why intervals are so effective, we need to delve deeper and look at what happens in muscle cells when they undergo interval training. Something that marks out interval training is that it tends to simultaneously tax the aerobic and anaerobic energy systems, and this may have a physiological bearing on why it’s so effective. Certainly, we know that even short sessions of interval training are able to significantly ‘remodel’ muscle cell function in quite profound ways. For example, researchers have found that a programme of interval training can(7): ●●Boost the capacity of muscles to utilise oxygen for energy production; ●●Increase the resting levels of glycogen in muscles (glycogen = stored muscle carbohydrate and your muscles’ preferred fuel for high-intensity exercise); ●●Increase the muscles’ ability to utilise fat for energy, which means they can conserve precious glycogen, thus extending endurance; ●●Enhance the circulation of blood and other nutrients to working muscles.
Exactly how these biochemical and structural changes occur is still a hot topic of research. However, recent research into the molecular basis of exercise points to a key signalling molecule called PGC-1α. PGC-1α is always present naturally in the body but levels of PGC-1α can be raised by certain types of exercise. Why is PGC-1α so important? Well, we now know that it can act directly on genes buried at the heart of muscle cells, stimulating those genes to manufacture more muscle mitochondria.
Muscle mitochondria can be thought of as your cells’ energy factories because they are able to harness the chemical energy from oxygen and convert it into a form your muscles can use for movement (ATP). The more mitochondria you have in a muscle cell, the better that cell becomes at producing energy, and when muscles cells are better at producing energy, they can work harder, for longer with less fatigue!
In very simple terms, then, the intense bursts during interval training are able to stimulate the production of PGC-1α, which then acts on ‘endurance genes’ buried in the cell nucleus, boosting their activity. As a result, these genes produce more mitochondria in muscle cells with the result that the muscles’
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figure 1: A molecular explanation of why intervals work!
the diagram above represents a muscle cell. performing some high-intensity interval training (Hit) activates 2 enzymes (ampK and p38mapK), a process that involves the interaction of phosphate groups (denoted by red ‘p’s) released during the exercise. these enzymes then stimulate the release of pGc-1α by passing on their phosphates – the pGc-1α is then able to cross into the cell nucleus (where the cell genes lie) and ‘activate’ a number of genes that are responsible for the synthesis of mitochondria. this happens because pGc-1α boosts level of something called transcription factor (tf) for those genes. the tf ‘reads’ these key genes and uses their stored codes to synthesise mitochondria, which are released into the main body of the cell. more muscle cell mitochondria leads to a greater capacity to produce energy, which in turn means muscles being able to work harder for longer without fatigue setting in!
capacity to perform is enhanced. Figure 1 shows the processes involved in a little more detail.
Although PGC-1α plays a key role in producing the desirable biochemical changes seen in muscles following interval training, it’s not solely responsible. For example, we also know that intervals increase cardiorespiratory function because studies show that intervals also boost maximum oxygen uptake capacity (sometimes referred to as ‘VO2max’)(8). If more oxygen is reaching the muscles per minute then the systems that absorb and transport it around the body (lungs, heart, circulatory system) must be functioning more effi ciently too.
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Another physiological change that occurs as a result of interval training is that the arteries (the vessels that carry oxygenated blood to the muscles) become more ‘compliant’(9). In simple terms, they become more elastic and are better able to accommodate the demands for increased blood flow during exercise. Also, studies show that even small amounts of interval training significantly increases ‘endothelial function’ in the trained muscles(9). This means that the inner linings of the blood vessels that carry blood to working muscles become more efficient at regulating blood flow and controlling the volume of fluid, amount of electrolytes and other nutrients that pass from the blood into the muscle tissues.
Finally, it’s worth noting here that even a modest increase in muscle PGC-1α appears to provide the body with a number of more general health benefits, including improved glucose metabolism and antioxidant defence systems as well as increased resistance to inflammation. Add to this that interval training has been shown to safely improve cardiorespiratory fitness in a range of populations including those with coronary artery disease, congestive heart failure, middle age adults with metabolic syndrome and obese individuals, and it’s easy to see why many researchers now regard interval training as the ideal exercise for everyone – not just sportsmen and women seeking to improve performance. However, this is a topic we’ll discuss in depth later in this report!
References 1. Appl Physiology, Nutr Metab, 2008; 33 (6): 1112–1123 2. Journal of Physiology, 2006; 575 (3): 901–911 3. European Journal of Applied Physiology, 2003 89 (3–4): 337–43 4. J Strength Conditioning Res, 2007; 21 (1): 188–92 5. Med Sc Sports and Exercise, 2007; 39 (4): 665–71 6. Journal of Science and Medicine in Sport, 2007; 10 (1): 27–35 7. J Physiol 590.5, 2012; pp 1077–1084 8. Metabolism, 2010; 59, 1421–1428 9. Am J Physiol Regul Integr Comp Physiol, 2008; 295 R236–R242
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Anatomy of interval training
So far, we’ve looked at how interval training evolved and why it’s such an effective form of training. In this section, we’re going to take a look at the structure of an interval programme and the different methods of adjusting rest and work periods to produce different types of interval programmes.
Warming up and cooling down Before we get down to the nitty gritty, it’s important to briefly discuss two extremely important elements of an interval training session, which are unfortunately often overlooked – the warm-up and cool-down. The very nature of intervals entails periods of relatively intense work. And given that these work periods are relatively intense, you need to prepare your body in readiness – ie warm up! A thorough pre-interval warm-up is vital for the following reasons: ●●It will make the intervals that follow feel easier to perform ●●It will allow you to work harder ●●It will reduce the severity of any post-exercise muscle soreness (sometimes referred to as DOMS) ●●It will reduce the risk of injury ●●Whatever else you include in an interval session, you should never skip a warm-up (see box 1 below)!
A proper cool-down is also an essential element of an interval session. Performing intervals will result in much higher accumulations of naturally occurring by products (eg lactic acid, protein fragments etc) in muscles. Cooling down helps to flush these by products out of muscles into the general circulation where they can either be metabolised or disposed of. Without a cool-down, these by products take longer to dissipate from your muscles, which results in an increased level of muscle fatigue and slower recovery times. Another good reason to cool down is to prevent ‘blood pooling,’ Stopping suddenly after intense exercise can result in large volumes of blood ‘stuck’ in the muscle tissue (blood pooling), especially in the legs. This in turn can cause symptoms such as nausea, dizziness and even fainting. As a rule of thumb, the longer and more intense your intervals are, the longer your cool-down needs to be (box 1).
Dissecting an interval Let’s look more closely at how we can manipulate an interval programme and start with considering the work intervals. There are three basic ways of adjusting the work intervals in an interval programme. These are:
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●●The interval length ●●The interval intensity ●●The number of interval repeats
Adjusting the length of each can be done in two ways – by time duration or distance duration. So for example, an accomplished runner training on a treadmill might decide to perform six intervals, each of one minute duration. However, the same runner training on the track might prefer to perform six intervals, each of 400m. Providing the duration and intensity of the intervals are not too dissimilar, it doesn’t really matter from a physiological viewpoint which method is used.
In some sports such as swimming, distance intervals are almost always used simply because it’s pretty inconvenient finishing an interval halfway down the pool! In other circumstances such as training on an indoor bike, it’s much more common to set duration by time since the distance shown by the computer on a stationary bike rarely correlates accurately to that covered at an equivalent power output on a real bike.
The number of interval repeats is of course easy to measure, providing you can count and have some degree of short-term memory!
Interval intensity can also be adjusted in different ways: ●●Speed ●●Power ●●Heart rate ●●Perceived effort level ●●Gradient
Speed Increasing any of the above will result in a more intense interval; the method you choose will often depend on your circumstances. On a road bike fitted with a bike computer for example, using speed as a way of setting intensity is easy; modern bike computers are pretty accurate and reliable, ensuring all the intervals are of equal intensity. When doing running intervals however, using speed is only really on option if you’re on a treadmill or you have a suitable GPS device for outdoor use.
Power On a stationary bike or rowing ergo, either power output or speed is likely to
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Box 1: Warming and cooling down – how to The key to a successful running warm-up is heat. I’m not talking about ‘in front of a log fire sipping hot chocolate’ sort of heat, though! I mean the sort of internally generated heat produced by a short period of pulse-raising aerobic work. This heat-producing activity should be considered as the core of a warm-up. For normal-paced training, as little as 5-10 minutes of gentle aerobic exercise (preferably the same type that you will be doing in your intervals) performed at around 55-60% of your maximum heart rate (MHR; [MHR = 220 – your age in years]) will produce a significant amount of internal heat – enough to help muscles and joints become prepared for the harder work ahead. For an interval training session, however, the demands on the body are higher, which means a more thorough warm-up is required. Although there are no universally agreed guidelines, you should reckon on spending at least 15 minutes warming up, with the last 10 of those minutes spent at around 60% of MHR. So for example, a 40-year-old cyclist preparing for an interval session should cycle gently before commencing the intervals for at least 15 minutes. The first 5 minutes of this warm-up could be at 55% of MHR (around 100 beats per minute [bpm]) while the next 10 minutes should be at around 60% of MHR (nearer 110bpm). With a cool-down, the idea is to gradually lower the heart rate until it drops to around 50% of MHR while still keeping moving. This helps restore normal blood flow and aids in removing the by products of intense exercise from the working muscles. In the example of our 40-year-old cyclist above, he or she should keep pedalling for 5-10 minutes gradually reducing the speed/ workload right down until the heart rate drops to near 90bpm.
be a good choice; while speed on an ergometer might not correlate accurately to speeds on the road or water, at least there’s likely to be consistency between intervals. Using the power output method to determine intensity can be very useful on a road bike but you’ll need an accurate powermeter device and these are expensive, typically costing many hundreds of pounds. However, for some sports such as running and swimming, there’s no way of accurately determining power output so it’s not an option.
Heart rate Of all the methods to control interval intensity, heart rate is the most universally applicable across all sports. This is because of the fairly linear relationship between heart rate and power output – you can think of your heart rate as a kind of ‘built-in powermeter’! As long as you know your maximum heart rate, you can set your interval intensity using % of MHR using different formulae
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(see box 2). Moreover, it’s very easy to track your heart rate in real time with a heart rate monitor.
Modern heart rate monitors are accurate and inexpensive and will work in a variety of environments – even water! There is however a big caveat here, and that’s due to the ‘lag’ in your heart rate response. Step on the gas to up your intensity to near maximum and it’ll take a while for your heart rate to respond. The fitter you are, the more rapidly it’ll respond, but even the fittest athletes will find their heart rates can take up to a minute to fully respond. What this means in practice is that gauging intensity by heart rate becomes pretty impractical for shorter intervals (under 2 minutes); by the time your interval is over and it’s time to rest, your heart rate may still be climbing and nowhere near the target you set! And that’s unfortunate because, as we’ll see in a later chapter, short and intense intervals have much to commend them.
Perceived effort level There are times when it’s impractical to use speed, power or heart rate to set interval intensity – for example, if you’re running or cycling in unfamiliar terrain with no electronic gadgetry to hand, or swimming without a heart rate monitor. The good news is that studies have shown your perceived level of exertion is a fairly decent measure of how hard you’re working and fairly reproducible too. A good way to use perceived rate of exertion (PRE for short) is to refer to the ‘Borg scale’ (see table 1) during your intervals. So for example, if you were performing, intense 30-second intervals, you might set your effort level at around 18 – very hard to very, very hard.
Gradient One final method to control interval intensity worth mentioning is that of gradient. If you ride or run over hilly terrain, you are in effect already performing a loose form of interval training. Maintaining a reasonably steady pace up a hill will dramatically increase your work rate as gravity takes its toll and some athletes find that ‘conquering’ a hill is a more rewarding way to perform intervals. But because hills come in all gradients and lengths and are unlikely be repeated at ideal time intervals, a better way is to find one hill and simply perform hill repeats. Powering up the hill provides the work interval while a slow descent provides an effective rest. Runners who have access to a programmable treadmill can construct a tailor-made hill interval programme by setting the gradient(s) they desire, the hill length and rest period!
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Box 2: Using heart rate formulae
If you’re using heart rate as a way of determining intensity, there are a couple of things to bear in mind. First, while maximum heart rate (MHR) is often quoted as ‘220 – your age in years’, it’s important to realise that this is an approximation. Your actual maximum heart rate can only be properly determined by performing a graded test to exhaustion – ie by working harder and harder until you can no longer keep going and seeing what your heart rate at that point is. If you choose this method to determine your MHR, be aware that it’s extremely unpleasant! Also, it’s most definitely NOT recommended for anyone who is not already extremely fit because of the (very small) risk of a cardiac arrest. MHR test can be carried out on older, less fit individuals, but they need to be done under medical supervision. The second point worth bearing in mind is that the widely-used formula for determining what heart rate to work at is itself rather over simplified. Working at 70% of MHR won’t necessarily mean that you’ll be working at 70% of your maximum sustainable power output. You can understand this better by considering the Karvonen formula instead. The Karvonen formula is a different way of calculating your training heart rate based not on a percentage of your absolute heart rate, but on your heart rate reserve – ie the amount of capacity your heart has to do work above and beyond its resting work rate. To calculate your heart rate reserve, you need to know your age, and your resting heart rate. Suppose your resting heart rate is 60 beats per minute (bpm) and your age is 36. Your maximum heart rate is still calculated as 220 – your age ie 184bpm. But your heart rate reserve is now given as the difference between rest and maximum heart rate, or 184 – 60bpm = 124bpm. If you work at 75% of your heart rate reserve, you’ll be training at 75% of 124bpm over and above your resting heart rate ie 93bpm above 60bpm, which is 153bpm. At 80% of heart rate reserve, it’s 80% of 124bpm over and above resting heart rate, which is 99bpm above 60bpm or 159bpm. Your training zone therefore is 153bpm – 159bpm. Although it’s slightly more complex to apply, the Karvonen formula more accurately reflects the working % of your maximum oxygen uptake than does a simple % of MHR calculation, particularly for fitter people. So, for example, you’re much more likely to be working at 75-80% of your maximum aerobic capacity at 153-159bpm than you are at 138-147bpm. This is why Karvonen- calculated training heart rate zones are often preferred to simple MHR calculations in those who train regularly and who are seeking a more accurate estimation of their ideal training heart rate.
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Table 1: Borg’s Perceived Rating of Exertion scale
SCALE NUMBER PERCEIVED EFFORT LEVEL APPROXIMATE HEART RATE
6 REST 60-70
7-8 VERY, VERY LIGHT 80
9-10 VERY LIGHT 100
11-12 FAIRLY LIGHT 115
13-14 SOMEWHAT HARD 130
15-16 HARD 150
17-18 VERY HARD 160-170
19 VERY, VERY HARD 180
20 TOTAL EXHAUSTION MAXIMUM HEART RATE
This scale uses a simple numbering system from 6 to 20 to rank the level of effort, with 6 equating to rest and 20 to total exhaustion. Borg adjusted the scale so that multiplying the scale number by 10 would roughly give someone’s exercising heart rate.
Examples The last few paragraphs will have hopefully given you a clear idea of how to assemble and control your work intervals. However, below are some examples of how these principles can work in practice.
Interval training workout (using heart rate and 2-minute intervals) i. Warm up for 10-15 minutes at the intensity described above. ii. Increase your workload/pace/speed/gradient by 20% for 2 minutes so that your heart rate reaches 85-90% MHR. iii. Drop your workload to 20% below your warm-up level for 1-2 minutes to allow recovery. iv. Repeat steps ii and iii 4-8 times. v. Warm down as above. Variations – try altering the ratio of work to recovery periods; try longer intervals at less intensity or shorter, more intense intervals.
Incline workout (on treadmills) i. Warm up as above. ii. Increase gradient by predetermined amount (more for shorter intervals, less for longer ones) and perform for allotted time.
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iii. After each interval, walk/jog slowly on the flat for recovery. iv. Warm down as above Variations – start at small gradient increase and work up; pyramid the interval durations (eg 4 minutes first segment, 2 minutes second etc.).
Pyramid workout for rowers – good for: more advanced trainers, increasing anaerobic threshold, improving VO2 max, developing power. i. Warm up as above. ii. Using the power output setting on your monitor, increase power output by 10% (eg instead of 180 watts, aim for 200 watts) for 4 minutes. Do this by keeping the same stroke rate but increasing the resistance/power delivery to the oar. iii. Take 1 minute rest. iv. Repeat step iii but at 20% higher output for 2 minutes. v. Take 1 minute rest. vi. Repeat step iii but at 30% higher output for 1 minute. vii. Now reverse the procedure i.e. reduce to 20% for 2 minutes then 10% for 4 minutes and finally back to start intensity (don’t forget your 1 minute rests!). viii. Cool down as above. Variations – there are hundreds! You can alter the jump in intensity (e.g. increase by just 5%), the length of each pyramid stage (e.g. you could do 8-4-2- 4-8 or 6-4-2-1-2-4-6 minutes), the amount of rest between stages, the way you increase work rate (e.g. you can keep the same resistance/power but use a higher stroke rate) and so on.
Mixed hill and pace intervals for runners (excellent for developing power, strength and running speed) i. Warm up as above. ii. Increase pace by 10% for 2 minutes iii. Recover until heart rate is back below 70% MHR. iv. Now increase gradient (not speed) by 2% for 2 minutes. v. Recover as in step iv. vi. Now increase both gradient and speed for 1 minute (ensuring that your heart rate does not exceed 90% MHR). vii. Recover as in step iv. viii. Now repeat steps iii to viii but using 20% for one minute in place of iii, 4% for one minute in place of v and combining the two for just 30 seconds in place of vii. ix. Repeat steps iii to viii at original settings. x. Warm down.
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Targeting energy systems At this point you should have a pretty good idea how to construct your work intervals in practical terms. But what is the best combination of work intensity and duration to choose? For example, should you be doing 30-second intervals at 95% maximum power, 60 second intervals at 90% maximum power or 2-minute intervals at 85% maximum power? To some extent, this question answers itself because the basic requirement of a work interval is to push the body out of its comfort zone (physiologically speaking).
To do this for short intervals, you will have to work pretty intensely. For longer intervals, you won’t need to work so intensely – indeed you won’t be able to because while you might be able to manage 8 x 95% efforts for 30 seconds, you’ll struggle to reach even 1 x 95% effort for 4 minutes! It also follows that short, low intensity intervals will be ineffective – 8 x 30-second intervals at 80% effort isn’t going to tax you because you can probably already sustain 80% effort for several minutes at a time! You can think of interval intensity vs. duration therefore as a seesaw, where as interval intensity rises, so the duration will drop and vice-versa.
Another approach is to consider the energy systems (see section – why intervals work). By choosing the energy system you want to target, you can get a feel for the interval length. For example, to challenge the phosphocreatine energy system, you’ll need relatively short intervals of 30 seconds or less; to challenge the lactate system, longer intervals of 1-2 minutes will be needed while aerobic type intervals usually comprise of even longer duration intervals.
Of course, all of the above is complicated by the fact that studies show a wide range of combinations of interval durations and intensities can produce good gains in fitness(1). Something else to bear in mind is that your current level of fitness will also play a role in determining what combination you use. An elite athlete might be able to manage 6 x 2-minute intervals at 95% MHR but this would be nigh on impossible for a recreational sportsman/woman or a novice. Finally (and as we hinted at earlier), new research suggests that short sessions of intense intervals can actually yield much greater fitness gains – particularly in aerobic fitness – than was previously realised. If time is tight that’s a big bonus, which is why we’ve devoted a whole section to this mode of training later in this report!
References 1. Appl Physiology, Nutr Metab, 2008; 33 (6): 1112–1123
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Rest and recovery
When the topic of interval training comes up, it’s natural to discuss how long and how hard each work interval is, and how many interval repeats are performed. That’s not surprising because we know that it’s the short bursts of relatively intense activity that are responsible for the benefits interval training brings. What’s often overlooked, however, is the rest interval, which is an integral part of the interval training process!
There are two key questions you need to consider when designing an interval programme: how long should you rest in between each interval and what kind of rest should you take? Should it be passive rest (where you simply stop and rest completely) or should it be active rest (where you slow right down to a very comfortable pace but still keep moving)? Let’s take the second question first and look at the pros and cons of passive and active rest.
Active or passive rest? On the face of it, the term ‘active rest’ might seem like a contradiction in terms. Surely, rest is just that – rest! In physiological terms however, the body can ‘rest’ and recover even during periods of light activity. Indeed, there are sound theoretical reasons why active rest between each work interval could be more advantageous than complete or passive rest.
One of these is that lying, sitting or even standing around motionless between each work interval will do little to promote enhanced blood flow to recovering muscles. This is in contrast to gentle activity, which produces sustained rhythmic movement in the muscles, stimulating blood flow and so helping to transport nutrients to and metabolic by-products away from recovering muscles. There’s another benefit of being more active during recovery; the rhythmic contraction of muscles helps to promote lymph drainage, which carries away waste products via the lymph system.
Benefits Some of these theoretical benefits have been borne out in scientific studies. For example, studies on runners have shown that active recovery immediately after hard intervals encourages recovery and reduces muscle lactate levels faster than complete rest (passive recovery). In one study on two groups of runners performing intense interval training consisting of 6-second bursts with 5-minute rest periods, one group rested completely while a second group exercised at 30% intensity between their intervals (active rest). The active group reduced blood
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lactate levels faster and achieved a higher average power output throughout their workout(1).
There’s good evidence that this faster rate of lactate removal is because of the increased flow of blood and oxygen in muscles during active recovery. An elegant experiment using Nuclear Magnetic Resonance Spectroscopy (NMRS) looked at the phosphate ions (from ATP) in the muscle fibres of male long distance runners(2). It showed that during active recovery after hard exercise, the acidity of the environment of the phosphate ions (acidity caused by an accumulation of lactic acid) dropped six times more quickly compared to passive recovery! The only explanation for this was the increased oxygen supply and efficient removal of lactate as a result of the greater blood flow.
There’s also good evidence that active recovery helps combat lactate accumulation from studies on swimmers(3). One study looked at swimmers who performed 10 x 200m flat-out intervals, each separated by 10 minutes of either active or passive rest. In addition, some swimmers recovered passively but with massage also given. The results were pretty unequivocal; the blood levels of lactate at the end of each rest period were lowest after active rest (5.72mmol per litre) and highest when passive rest was taken (10.94mmol per litre). And while the massage helped, it only lowered blood lactate to 7.10mmol per litre (see figure 1). Moreover, the swimmers who rested actively performed significantly better in the subsequent 200m bouts than those who rested passively.
Another (brand new at the time of writing) study has looked at the effects of active vs. passive rest periods within an interval training programme carried out by 24 male subjects(4). The subjects were split into three groups: a control group who did no interval training, an active recovery group who rested actively between intervals and a passive group who rested passively between intervals. Before and after the 3-week training programme, the researchers measured the maximal oxygen capacities of the subjects as well as their levels of stress hormones. The results showed that it was the active group who responded (ie made gains) in the maximal oxygen uptake test following the 3 weeks of training. However, the downside was that the active recovery seemed to induce more metabolic stress in the subjects.
Caveats Although a number of other studies have shown that active rest is more effective at helping to clear lactate and other by products of exercise from muscles than
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Figure 1: The effects on blood lactate of active rest, passive rest and massage in swimmers(3)
12
10
8
6
4 Blood lactate concentration (mmol/L) 2
0 1 2 3 Rest type Blood concentration of lactate after 10 minutes of differing rest type: 1= active rest; 2 = passive plus massage; 3 = pure passive rest
passive rest, not all studies have concluded that active rest yields superior results to passive rest. For example, a German study examined the effects of a 2-week high-intensity interval programme on maximal oxygen consumption and parameters of exercise performance in 16 junior triathletes(5). In particular, the researchers wanted to see how the results of this programme were influenced by the type of rest the triathletes took in between their work intervals.
The triathletes performed a total of 15 high-intensity interval sessions within three separate 3-day training blocks. Before and one week after the last training session, the athletes performed a graded exercise test to determine their maximum oxygen uptake capacities and a time trial during which power outputs were measured. The results showed that in terms of peak power output during the graded exercise test and time trial performance, all the triathletes made gains, regardless of the type of rest they took during intervals. However, it was the passive group triathletes who showed better endurance gains overall as they were able to sustain higher continual power outputs near their maximum oxygen uptake level.
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These results might seem surprising, especially given that the total workload of the passive rest group was less than the active rest group. However, one possible explanation is that this 15-day period of interval training was very intense compared to the triathletes’ normal schedules. The extra work involved in the active rest intervals therefore may have pushed them that bit further into a slightly overtrained state, which resulted in less fitness gains than they might otherwise have achieved.
Another study on rest type during intervals looked at team sports involving repeated short-duration sprints(6). Nine moderately-trained men, most of whom regularly competed in various team sports, performed four repeated-sprint tests on cycle ergometers (six 4-second sprints every 25 seconds), at weekly intervals. In two of the trials, the sprints were separated by 21 seconds of active recovery, which involved cycling at around 32% of VO2max. In the other two trials, the sprints were separated by passive recovery periods, in which the athletes did nothing. The researchers compared the athletes’ performances in the two sets of trials and also analysed samples of thigh muscle tissue before and after each of the four tests to check levels of phosphocreatine, creatine and lactate.
As expected, peak power outputs produced during sprints 2-6 were significantly lower than for the first sprint, regardless of what type of recovery was used. However, there was a significantly lower peak power output and a greater drop in power decrement for the sixth sprint with active recovery than with passive recovery. Moreover, muscle lactate levels were significantly higher and phosphocreatine somewhat lower after the tests involving active rest recovery showing poorer recovery between sprints.
Of course, it makes no sense in terms of sport and competition to suggest that team players should stand still between repeated-sprint bouts so the researchers still concluded that training for repeated-sprint performance should involve active rather than passive recovery periods. However, what this study did show is that active rest can have some negative impact on subsequent very intense intervals.
How long should my rest periods be? The fact that a period of active rest might negatively affect your ability to perform a subsequent flat-out sprint interval is perhaps not surprising. However, some research indicates that what really counts is the length of the rest period rather than whether it’s active or passive. In a 2011 study, British researchers looked
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at the effects of a constant sprint-to-rest ratio and different recovery modes on repeated sprint performance(7). Three repeated sprint protocols were used (22 x 15, 13 x 30, and 8 x 50 m), with each having an active and passive recovery. Three repeated sprint protocols were used (22 x 15m, 13 x 30m, and 8 x 50 m), each using both an active and passive recoveries between sprints and each protocol was conducted with an initial sprint-to-rest ratio of 1:10 (ie however long the sprint distance took, the rest between sprints was 10 x as long).
What became apparent was that in the 22 repeats of 15-metre sprints, sprint performance was didn’t change as the set progressed, regardless of which type of rest was used. In the 13 repeats of 30 metres, the last sprint was an average of 0.2 seconds slower than the first but again, this result was the same regardless of whether active of passive rest was taken. In the 8 x 50m sprints, the final sprint was on average 0.39 seconds slower than the first, but yet again, the type of rest taken was irrelevant. The key take-home point here is that if the rest interval is sufficiently long, it doesn’t seem to matter whether recovery is active or passive.
How should active recovery be performed? Interval training is likely to be effective regardless of whether your rest intervals are active or passive. However, it’s fair to say that on balance, there’s more slightly evidence in favour of active recovery during intervals, which begs the question of how best to perform active recovery. Unfortunately, there are no hard and fast prescriptions, particularly as what’s most appropriate will depend on the circumstances and your individual preferences. However, we can turn to research from swimming (a sport where much of the day-to-day training is based on interval work) for some useful pointers.
A group of studies conducted over a number of years by Greek researchers Department of Physical Education and Sport Science, Democritus University of Thrace makes for enlightening reading. In the first study, the scientists investigated the effect of different intensities of active recovery on performance during repeated sprint swimming(8). Nine male well-trained swimmers performed eight repetitions of 25m sprints (8 x 25 m) interspersed with 45-second intervals, followed by a 50m sprint test 6 minutes later. During the 45-seconds and 6-minute interval periods, the swimmers either rested passively or swam at an intensity corresponding to 50% and 60% of their individual 100m speed.
The first 25m sprint was not different across the trials, but performance decreased after sprint #2 during both the active recovery trials compared with the passive
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recovery trial (see figure 2). Performance time for the 50m sprint performed 6 minutes after the 8 x 25 m sprints however was no different between trials. These results indicate that 45 seconds of active recovery at intensities corresponding to 50% and 60% of the 100m velocity during repeated swimming sprints decreased performance even though blood lactate levels were lower. However, when a 6-minute recovery was given at the end of the sprints, active rest did not affect performance on a subsequent 50m sprint. The researchers concluded that ‘passive recovery is advised during short-interval repeated sprint training’ in well-trained swimmers. However, this study also showed that when the period of active rest was much longer, it was possible to recover fully for a (longer) 50m sprint.
In a follow-up study published in 2008, the same group examined the effects of active and passive rest periods of various durations after a 100m swimming test performed at maximal effort(9). The active rest comprised of swimming at 60% of the swimmers’ normal 100m speed. Eleven competitive swimmers completed two 100m tests at maximum swimming effort with a 15-minute interval under three experimental conditions:
Figure 2: Effects of active/passive rest on subsequent 25m swim sprint times (sprint #2 onwards)(8) 14
13.5
13
12.5
12
11.5 Time to perform subsequent intervals (seconds)
11 Passive Active 50% Active 60% Type of rest In the first 25m sprint, the recorded times were similar. But from sprint #2 onwards, the swimmers who performed active rest at either 50% or 60% of their 100m swim speed swum their subsequent 25m intervals significantly slower.
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●●15 minutes of passive rest ●●5 minutes of active rest/10 minutes of passive rest ●●10 minutes of active rest/5 minutes of passive rest
The result showed that blood lactate was lowest and the 2nd 100m was swum faster when the swimmers performed 5 minutes of active rest and 10 minutes of passive rest. Fifteen minutes of passive rest and 10 minutes of active/5 minutes of passive produced significantly slower times.
A third study followed a similar design to the 2006 study but this time looked at active recoveries performed at 40% and 60% of the swimmers’ 100m speeds(10). Ten male competitive swimmers performed 8 x 25m sprints with 120-second rest intervals followed by a 50m sprint 6 minutes later. During the 120-second and the 6-minute interval periods swimmers rested passively or swam at an intensity that corresponded to 40% and 60% of the oxygen usage of their individual 100-m velocities.
This time, 2 minutes of active rest at 40% of the swimmers’ 100m oxygen consumption values was equally as effective as 2 minutes of passive rest in allowing the swimmers to fully recover between the 25m sprints. The 60% active recovery protocol did not allow full recovery in between the sprints but did allow recovery for the 50m sprint 6 minutes later.
Summing up, what this study showed is that even when the rest duration was extended to 2 minutes (compared to 45 seconds in the 2006 study), 60% active recovery was still too vigorous to allow full recovery for repeated sprint performance. However, 40% active recovery was effective, indicating that both rest times and the intensity of active rest will determine recovery effectiveness during intervals.
Summary Once again, there’s a lot to take in here, so let’s try and summarise this section in order to give practical guidelines. Firstly, there’s no doubt that active rest does help reduce the accumulation of blood lactate during a set of intervals. There’s also no doubt that by resting actively, you’ll achieve a higher overall work rate during your intervals than if you just rest passively. There’s even some recent evidence showing that the overall effectiveness of intervals in enhancing aerobic performance could be greater when active rest periods are used, albeit at a cost of higher metabolic stress.
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However, there are a number of ifs, buts and maybes to consider too. The research on junior triathletes who performed a very intense period of interval training showed reduced gains in endurance performance. This suggests that active rest periods might not be best when training loads are very high because the extra workload they add to the total load could result in excessive metabolic stress. Also, active recovery during sprint intervals could be counterproductive if the rest periods are very short (as demonstrated in the team sport study). By contrast, when the rest periods are relatively long (as in the study on sprinters), active rest is just as effective as passive rest for recovery.
This principle also ties in well with the studies on swimming, which showed that passive recovery is preferred during short-interval repeated sprint training’ but that when the period of active rest was much longer, it was possible to recover fully for a subsequent effort. Indeed, when the rest period becomes long and the work intervals themselves are longer, it seems that some active recovery (to reduce lactate) is beneficial to the performance of those intervals. The key though seems to be to keep the intensity of active recovery very gentle.
In short, during very intense (sprint-like) intervals, rest periods need to be extended relative to the work interval and any active rest should be extremely gentle – indeed, passive may be better. For hard but not flat-out intervals, active recovery is likely to produce greater benefits!
References 1. Med Sci Sports Exerc. 1996 Apr;28(4):450-6 2. NMR Biomed. 1996 Feb;9(1):13-9 3. J Sports Med Phys Fitness. 2012 Apr;52(2):122-7 4. Int J Sports Med. 2013 Feb 26. [Epub ahead of print] 5. J Strength Cond Res. 2013 May;27(5):1384-93 6. Med Sci Sports Exerc, vol 38, no 8, pp1492-1499, 2006 7. J Strength Cond Res. 2011 Jun;25(6):1695-702 8. Appl Physiol Nutr Metab. 2006 Dec;31(6):709-16 9. Int J Sports Physiol Perform. 2008 Sep;3(3):375-86. 10. J Strength Cond Res. 2011 Jan;25(1):109-16. doi: 10.1519/JSC.0b013e3181b22a9a.
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High intensity interval: why less can be more!
So far in this report, we’ve answered a number of questions about the whys and wherefores of interval training. In this section, we’ll look more closely at high- intensity interval training. Why? Because recent evidence suggests that this mode of interval training delivers more training benefits in less time and with less effort. It seems you really might be able to have your cake and eat it...!
Introduction Earlier in this report, we looked at the very flexible structure of intervals (ie how the duration and intensity of intervals and rest periods can be manipulated) and how that flexibility enables different interval sessions to be targeted at the different energy systems required for a particular event. For example, 400m sprinting requires energy from both the phosphocreatine and lactate systems, so intervals designed to improve 400m performance would need to target both of these energy systems.
This principle of matching the interval length and intensity to the energy demands of your event makes sense, not least because it’s based on sound scientific principles. What’s extremely interesting however is that new research suggests that athletes can also benefit from interval training that doesn’t appear to fit this principle. Even more intriguingly, there’s good evidence that endurance athletes whose events rely primarily on aerobic energy production – eg distance runners, cyclists, rowers, swimmers etc – can actually benefit greatly from short, intense interval sessions.
In the beginning The birth of high-intensity interval training (HIT) as a productive mode of training for endurance athletes stems from earlier research by a Japanese professor called Izumi Tabata of the National Institute of Fitness and Sports in Kanoya, Japan. In a revolutionary study published in 1997, Tabata Tabata designed a scientific study for a protocol that was already being used by Japanese speed skaters(1).
Tabata’s study compared two groups of athletes over a 6-week period. In the study, the first group of athletes engaged in one hour of steady-state, moderate- intensity (70% of maximum oxygen uptake – VO2 max) endurance training on a stationary bicycle for five days each week. The second group, meanwhile,
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followed a protocol similar to the one already being used by Japanese speed skaters. This second group also did their work on a stationary bicycle but with a very different structure: after a 10-minute warm-up, they engaged in a 4-minute period of eight intervals with a 2:1 ratio between work and rest (ie 8 sets of 20 seconds of work followed by 10 seconds of rest).
During the work phase, intensity was kept very high at 170% of VO2 max (in other words, at an intensity well in excess of what the athletes could have sustained over a longer period) with pedalling speeds at 90 rpm. If pedalling speed dropped below 85 rpm, the set was ended. If an athlete could complete nine sets at 90 rpm, then the resistance was increased so as to require 11 watts of additional work during the work sessions. This interval training was then followed by a cool-down period. One day a week the protocol was changed to allow for 30 minutes of moderate intensity (70% of VO2max) steady state training, followed by 4 rounds of 20s of high intensity work followed by 10s of rest.
When the researchers analysed the results, the first finding was that (perhaps unsurprisingly), the Tabata method of training resulted in improvements to the athletes’ anaerobic capacity whereas the steady-state trained athletes made no such gains. Given that the Tabata-trained athletes worked for short periods of time at levels that greatly exceeded their aerobic capacity – ie trained anaerobically – this makes perfect sense (remember what we said about targeting energy systems).
However, what fascinated the researchers was that the Tabata-trained athletes also made substantial gains in VO2max, particularly during the first half of the experiment. This indicated that the very short, high-intensity protocol had actually been able to boost aerobic endurance as well as anaerobic performance! And while these aerobic gains were no greater than the gains achieved by the steady state group, it’s worth noting that the experiment started with a significant gap in VO2max between the two groups, with the Tabata group recording significantly poorer scores of VO2max. Over the course of the six weeks, however, the Tabata- trained group was able to narrow that gap significantly!
The key finding from this study is that HIT can produce good gains in aerobic fitness even though the training itself is not what we would think of as aerobic type training. In addition, it showed that HIT also provides anaerobic benefits for athletes, which cannot be achieved with steady state aerobic exercise alone. A third (and very important) benefit of this mode of training was that compared
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to the steady state group, less time was required to produce equivalent aerobic gains. Tabata concluded that his protocol worked because it was able to stress both the aerobic and anaerobic energy releasing systems maximally. While this is true, in the years since, scientists have begun to understand the processes involved at a much more fundamental (molecular) level – see section two.
Recent research into HIT Tabata’s training findings were groundbreaking because if confirmed, they seemed to offer great advantages to athletes. Firstly, this type of short, intense interval training doesn’t take up too much time and is not too exhausting to fit into a busy training schedule. There’s also a huge psychological advantage; the prospect of a long, hard interval session can be daunting, especially when athletes are tired. A brief, intense session of intervals, on the other hand, is likely to be far more appealing if it can deliver decent gains for not too much pain! Given these potential advantages, it’s not surprising that this is an area that has been researched extensively in more recent years.
A good example of this recent research is a study in which Swedish scientists looked at the effects of two types of cycling sessions on genetic markers for mitochondrial biogenesis in elite cyclists(2). Mitochondria can be thought of as the ‘aerobic energy factories’ within our cells. All other things being equal, a higher density of mitochondria in muscle cells means a higher aerobic capacity. An increase in these genetic markers of mitochondria synthesis essentially means the genes are ‘switching on’ the process of making new mitochondria in cells.
In the study, ten male cyclists competing at national level (average VO2max of 68mls/kg/min) performed the following cycling protocols: ●●7 x 30-second ‘all-out’ bouts (sprint intervals); ●●3 x 20-minute bouts at around 87% of VO2max (long-duration aerobic intervals).
During long intervals, the total work performed was 8 times greater and the exercise duration 17 times longer than during the sprint intervals. Muscle samples were taken before and three hours after exercise in order to measure the changes in levels of genetic markers of mitochondria synthesis.
The results were rather surprising; the post-exercise increase of three key markers of mitochondria synthesis (PGC-1alpha, PRC and PPARdelta) was just as large after the sprint intervals as the long intervals. Moreover, a fourth marker (Tfam) was only raised after the sprint interval training – not after the long intervals.
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The fact that the key genetic markers were elevated similarly after both short, low-volume sprint intervals and longer (more traditional) aerobic type intervals indicates that the short sprint intervals were just as effective at increasing mitochondria density, which is a key determinant of aerobic performance.
Triathletes and short intervals These results are completely contrary to what the researchers had expected (ie that only long ‘aerobic type’ intervals can produce an increase in aerobic capacity of muscles) but they do seem to fit with other recent findings – namely that short, high-intensity intervals can benefit aerobic performance. For example, a very recent US study on triathletes also supports the notion that when it comes to intervals, less can be more(3).
In the study, the researchers compared the effects of four different interval- training regimes on 12 recreationally competitive male and female triathletes. The subjects performed four different types of interval sessions on a cycle ergometer, which were as follows: 1. 90% of maximum power output for 30 seconds; 2. 90% of maximum power output for 3 minutes; 3. 100% of maximum power output for 30 seconds; 4. 100% of maximum power output for 3 minutes.
Measurements were taken to see how each type of interval session affected oxygen uptake, biomarkers of fatigue such as blood lactate, rating of perceived exertion and also the total time in the high-intensity zone that each triathlete could accrue.
The researchers found that compared with the 3-minute intervals, the 30-second intervals allowed the triathletes to perform longer overall sessions, with higher total and average oxygen consumption levels. Compared to 100% maximum power, the 90% maximum power intervals also allowed the triathletes to perform longer sessions with higher total oxygen consumption.
The researchers concluded that the best way to increase the total time spent at high intensity during intervals and maximise oxygen uptake (ie maximise the training effect) is to perform short (30-second) intervals at 90% maximum power rather than to perform longer, harder efforts.
Just ten seconds The fact that interval sessions consisting of intervals lasting just 30 seconds
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was of more benefit to the performance of triathletes than 3-minute intervals is surprising enough. However, another very recent Canadian study suggests that even shorter intervals of just 10 seconds can benefit aerobic performance(4)! In the study, 48 subjects were split into four groups following different interval training protocols on a cycling ergometer. These were: 1. 30-second interval, 4 minutes rest (average intensity 89% of peak power) 2. 10-second interval, 4 minutes rest (average intensity 96% of peak power) 3. 10-second interval, 2 minutes rest (average intensity 95% of peak power) 4. no training (control group)
The subjects trained three times per week for two weeks. Each session initially consisted of 4 intervals, but this was raised to 6 intervals over the 2-week period. Before and after the study, the subjects’ maximum oxygen uptake, 5km time-trial and maximum power outputs were measured.
The researchers found that all three interval protocols produced gains in maximum oxygen uptake, 5km time-trial performance and maximum power outputs. The aerobic, time trial and peak power gains were greatest in the 30-second interval group but still significant in both of the 10-second groups. Peak power gains were similar in the 30-second and 10-second/4 minutes rest groups but somewhat lower in the 10-second/2 minute rest group. This study provides further evidence that 30-second intervals can be very effective for endurance performance gains, but what’s remarkable is that it also shows intervals as short as 10 seconds can still produce real performance gains!
The sweet spot – 30/90 So far, we’ve looked at three recent studies suggesting that interval training using 30-second intervals can be of real value for endurance athletes such as runners, cyclists, triathletes etc. In two of these studies, an interval intensity of around 90% of peak power seemed to produce the greatest gains(3,4) and other studies have indicated that 90% peak power intensity for intervals is effective.
For example, a Norwegian study on trained cyclists found that shorter intervals pedalling at 90% maximum intensity produced better performance gains (in terms of the maximum power that could be sustained for long periods) than cycling at a maximum intensity of 88% using intervals twice as long(5). However, when the researchers halved the interval time again but asked the cyclists to compensate by pedalling at 94% of their maximum intensity, they found that performance actually fell.
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The key point here is that while short intense intervals can be very effective, if the intensity is too high for too long, the results can be counterproductive. It’s true that in the Swedish study above(2), the subjects got excellent gains pedalling ‘flat out’, which might seem to contradict the ‘90% sweet spot’ evidence. However, it’s worth remembering that these were elite national level cyclists who were probably far more used to flat-out sprinting. Moreover, if they had been asked to perform 90% effort intervals, they may have still achieved the same or even greater gains.
The bigger picture For many endurance athletes, there’s a reluctance to contemplate the use of high-intensity intervals. One of the main reasons for this is that this type of training is normally associated with explosive power or sprinting ability, neither of which are of primary importance for endurance events. As we have seen, however, there’s good evidence that some high-intensity interval training can be of great value for aerobic performance.
The example of teenage swimmers illustrates this quite well; many swimmers of this age spend in excess of 15 hours per week in the pool and studies have shown that a great portion of the weekly training volume is usually performed at lower intensities(6). However, a 2008 study of 16-year old swimmers examined the effects of 4 weeks of low-volume, high-intensity interval training on swimming performance and compared it with high-volume endurance training(7). The results showed the low volume, high-intensity interval protocol to be equally effective in terms of improving swimming performance but with the benefits of a lower total training load.
Of course, this is not to say that the core of an endurance-training programme shouldn’t be aerobic based; it should, and lower-intensity (70-75% maximum heart rate) aerobic work should still comprise the bulk of any endurance athlete’s workload. However, the crucial point is that the high-intensity interval work should be just that – high intensity. In a way, this fits in very neatly with the theory of ‘polarised training’ (see box 1). This theory states that endurance athletes should emphasise mainly low-intensity aerobic training with some very high-intensity training, while not spending too much time performing moderate-intensity training (which targets the lactate energy system).
Short vs. long intervals Finally, if you’re still convinced that only long, ‘aerobic type’ intervals can deliver the goods when it comes to aerobic performance, it’s worth considering a 2012
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Box 1: Polarised training theory The polarised theory of training uses the concept of ‘intensity zones’. Basically, this concept assigns your time spent training into three zones – 1, 2 and 3 – which refer to easy, moderately hard and extremely hard intensities of training respectively (see below). What’s fascinating is that studies on elite athletes such as runners and rowers suggest that the best way of achieving your maximum endurance potential is to spend the bulk of your training time in zone 1, ensure you spend at least some time in zone 3 but not to spend too much time in zone 2 (the moderately hard zone).
Sometimes Typical blood Zone known as: Subjective feel: lactate levels Typical heart rate 1 ‘Aerobic’, ‘easy’, Easy – you feel like Less than Under 80% and ‘recovery’, ‘long you can keep going 2mmol per litre typically around 70- slow distance’ etc and going 75% of maximum
2 ‘Threshold Moderately hard Between 2 and Around 80-85% of training’, – hard (you know 4mmol per litre maximum ‘intensive you’ve had a endurance’ etc workout)
3 ‘Very high Very, very hard (you More than Significantly over intensity’, ‘race won’t want to stay in 4mmol per litre 85% of maximum pace’ etc this zone for long!)
study on 40km time trial performance in male cyclists(8). In the study, well-trained cyclists were randomly assigned to one of five different interval training protocols: ●●12 x 30 seconds at 175% of peak sustained power output (PPO) ●●12 x 60 seconds at 100% PPO ●●12 x 2 minutes at 90% PPO ●●8 x 4 minutes at 85% PPO ●●4 x 8 minutes at 80% PPO
All the cyclists completed six HIT sessions a week over a 3-week period in addition to normal aerobic base training.
As figure 1 shows, the researchers discovered that the 30-second intervals were pretty much as effective as the 8 x 4-minute protocol, and were far more effective that 1, 2 or 8-minute intervals! This is even more surprising when you consider that a 40km time trial relies almost exclusively on aerobic power (a club cyclist will typically take around an hour to complete this distance) and also consider that the 30-second interval sessions involved just 6 minutes of work whereas the other protocols involved between 12 and 32 minutes of work!
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Figure 1: Interval length and intensity vs. endurance gains(8)
4
2
40 km speed (%) 0
-2 Duration (min) 0.5 1 2 4 8
Intensity (%PPO) 175 100 90 85 80
Shows how the 0.5-minute intervals were as effective as 8 x 4-minute intervals in increasing 40km speed (by around 2-4%) and more effective than the other three protocols.
Short intervals for everyone? High-intensity intervals work – no doubt about that, However, while athletes are accustomed to very intense bursts of efforts, this is unlikely to be the case for those who are simply trying to get a bit fitter and healthier. That being so, some researchers have been focussed on developing a form of interval training that is less intense than the Tabata protocol but retains most of the benefits, while being safe enough to incorporate into general fitness training.
In a 2010 study, Professor Martin Gibala from McMaster University in Canada was able to demonstrate that intense interval training does not have to be ‘all out’ in order to be effective(9). His study showed that performing 10 x 1-minute sprints on a standard stationary bike with about one minute of rest in between, three times a week, works as well in improving muscle as many hours of conventional long-term biking performed less strenuously. What was interesting in this study was that it used a standard stationary bicycle and a workload which, while still above most people’s comfort zone (about 95% of maximal heart rate), was only about half of what can be achieved when people sprint at an all-out pace.
Importantly, this less extreme HIT method seems to work well for less athletic people (the older, less fit, and slightly overweight) whose doctors might have worries about them exercising intensely. This in turn has very positive
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implications for health, and that’s something we’ll look at later in this report!
Summary and practical recommendations Okay, there’s quite a lot of information here so what are the key points and how can you apply the recent findings about HIT in your own training to maximise performance? Here’s a summary and some recommendations: ●●Shorter, intense intervals are the natural choice of sprint/power athletes because the demands on the energy systems are closely matched. However, recent research suggests that short, intense interval sessions can also benefit endurance athletes – as well as improving endurance performance, they allow athletes to make performance gains with a lower total training load. ●●There’s no universal agreement on the optimum length, intensity and numbers of intervals but studies using 4-8 intervals of 30 seconds at around 90% maximum power output have produced good results. ●●Intensities lower than 90% maximum power output may not be high enough to produce gains in a 30-second interval routine. There’s also evidence that significantly higher than this (over 95% of maximum power) may be less effective (possibly because the significantly increased training load starts to become counterproductive). ●●The total volume of time spent training doesn’t necessarily correlate to the gains produced; in effect this means that endurance athletes may well get better performance gains by cutting out some of their long, slow distance work in order to make way for some intense intervals. ●●Beware of performing too many longer (lactate threshold) interval sessions. The evidence suggests that too much lactate threshold work is counterproductive – possibly because it imposes a high training load (making big demands on recovery) yet without maximising the training stimulus.
References 1. Med Sci Sports Exerc 1997; Volume 29(3), pp 390-395 2. Eur J Appl Physiol. 2010 Oct;110(3):597-606 3. J Strength Cond Res. 2011 May;25(5):1279-84 4. Eur J Appl Physiol. 2010 Sep;110(1):153-60 5. Scand J Med Sci Sports. 2011 Aug 3. doi: 10.1111/j.1600-0838.2011.01351.x 6. Int J Sports Med. 1998;19:439–446 7. Int J Sports Med. 2008 Nov;29(11):906-12 8. J Physiol 590.5 (2012) pp 1077–1084 9. The Journal of Physiology, 2010; DOI: 10.1113/jphysiol.2009.181743
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Intervals: good for health as well as performance!
Interval training has traditionally been regarded as something that elite sportsmen and women do to enhance performance. However, in this section we’ll look at emerging evidence that intervals provide health benefits – not just for athletes but for anybody seeking to get a bit fitter and stay healthy!
Most people associate intense exercise with elite athletes rather than Joe Public and that’s perhaps not surprising. After all, the oft repeated mantra doctors and other health professionals is that gentle-moderate exercise is the kind recommended for health. Intense or very vigorous exercise on the other hand tends to be regarded much more as the preserve of the younger, competitive sportsman or woman.
It’s easy to see how this consensus has arisen; a number of studies have shown that 30 minutes of gentle-moderate exercise performed on most or all days of the week may result in a reduction in the risk of cardiovascular disease. Meanwhile, well-documented cases of sudden cardiac death as a result of unusually vigorous exercise abound – witness the case of the footballer Fabrice Muamba in 2012. Had he not had immediate expert medical attention, he would have almost certainly died as a result of his heart attack. Hardly surprising then that many health professionals see intense exercise as not only unnecessary, but even as something to be avoided.
Intense is best However, there’s a problem with this approach – it’s wrong! Several large studies have found that the rates of death from coronary heart disease (CHD) and all- cause mortality (rates of death from any condition) are lower among vigorously active individuals than among moderately active individuals. For example, in a nine-year study of 18,000 British civil servants, the CHD rate among office workers who took part in swimming, running and other vigorous activities was less than half the CHD rate of office workers who reported no vigorous exercise(1,2). This same pattern was observed in smokers, those with high blood pressure and those with a family history of CHD, suggesting that vigorous exercise exerts protection independent of other risk factors.
In a famous study known as the Harvard Alumni Health Study, the relationship
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between physical activity and CHD was assessed at different time points in men who enrolled at Harvard University between 1916 and 1950. Baseline and follow-up questionnaires sought information about walking, stair climbing and participation in sport and exercise. The early results showed that in the 17,000 men followed for over 20 years, there was an inverse relationship between physical activity and all-cause mortality(3). In other words, the less physical activity, the greater the rate of all-cause mortality. Importantly, however, participation in non-vigorous (ie gentle-moderate) exercise was not associated with an increased lifespan. The researchers subsequently concluded that ‘a half hour of vigorous activity expends as much energy as moderate activity carried out for twice or three times as long – and it can provide greater heart health benefits(4).’
Another important study known as the ‘Health Professionals’ Follow-up Study’ is noteworthy because of its large sample size and its rigorous methodology(5). The subjects consisted of 44,500 health professionals, from dentists to veterinarians, aged 40–75 years, who were followed from 1986 to 1998. Their levels of physical activity were assessed at baseline and then at two-year intervals using a questionnaire.
The results showed that the risk of CHD was reduced by 18% in those who walked 30 minutes per day but more encouragingly, CHD risk was reduced by 42% in men who ran for one hour per week. Moreover, men who consistently engaged in any form of vigorous exercise enjoyed a 30% reduction in CHD risk compared to men who maintained a lower intensity of exercise. Interestingly, men who increased their exercise intensity from low to vigorous enjoyed an extra 12% reduction in CHD risk. This study of health professionals reached a similar conclusion to that of Harvard alumni: while gentle-moderate intensity exercise such as brisk walking or slow jogging may reduce CHD risk, greater protection can be gained by engaging in more intense exercise.
Figure 1 shows the relationship between physical fitness and cardiovascular mortality and between physical fitness and all-cause mortality(6). The ‘fitness quintiles’ numbered 1-5 rank fitness with fitness quintile #1 being the lowest fitness bracket, fitness quintile #5 the highest, with the intermediate quintiles representing the 20% fitness brackets in between. You can see that individuals with fitness levels in quintile 4-5 have by far the lowest risk of CHD and early death from any cause.
But now think about this: to enter fitness quintile #2 and enjoy any protection
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Figure 1: The risk of mortality from CHD and all causes ranked by fitness quintiles(6)
70 All-causes 60 Cardovascular disease
50
40
30
20 Mortality per 10,000 man years
10
1 2 to 3 4 to 5 Fitness quintiles from disease, someone aged 40–49 years would need to have an aerobic capacity of 11 METs31. However, one MET is equivalent to the energy expended at rest, and brisk walking requires only 4 METs. You can hopefully see therefore that while gentle/moderate intensity exercise will gain you some health benefits, much greater benefit can be had with higher levels of aerobic fitness, for which much more intense exercise is required. And that’s where interval training comes in because, as we’ve said previously, interval training is an extremely efficient and manageable way of increasing exercise intensity and building aerobic fitness!
Why does interval training benefit health? There are a number of reasons why vigorous exercise is more effective in fighting conditions such as obesity, type-2 diabetes and coronary heart disease, all of which can lead to early death. We know that weight loss occurs when energy expenditure exceeds energy intake. Because vigorous exercise burns more calories per minute than moderate-intensity exercise, it offers an advantage in controlling weight.
In a 2003 report, the International Association for the Study of Obesity
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concluded that 30 minutes of moderate activity per day was insufficient to prevent unhealthy weight gain(7). Instead, the expert panel concluded that 60–90 minutes of moderate activity per day or ‘lesser amounts of vigorous activity’ was needed to prevent weight regain in formerly obese individuals.
Fat burning, insulin and type-2 diabetes We also know that aerobic exercise increases the ability of the hormone insulin to work in the body, which is needed to lower blood sugar and prevent type-2 diabetes. However, recent research has shown that the ‘insulin-sensitising’ effect of exercise is far greater during vigorous exercise than during moderate exercise(8). In fact it’s likely that any exercise actually needs to be pretty intense in order to deplete muscle glycogen (stored muscle carbohydrate) and therefore increase insulin sensitivity(9). This is probably because when muscle stores of glycogen are depleted during intense exercise, signalling molecules are released, increasing the muscle cells’ sensitivity to insulin and thus helping to restore muscle glycogen more rapidly when carbohydrate is eaten.
A good example of these benefits in practice can be seen in a study by researchers at McMasters University in Canada published in 2011(10). Gibala and his team investigated a low-volume HIT protocol on skeletal muscle oxidative capacity and insulin sensitivity in middle-aged adults, who are often at a higher risk for inactivity-related disorders. Seven sedentary but otherwise healthy individuals performed six training sessions during a 2-week period. Each session involved 10 x 1 minutes of cycling at around 60% of peak power equating to an intensity that produced 80%-95% of heart rate reserve (ie relatively intense but not flat out), with 1 minute of recovery between intervals. The results showed that the ability of the subjects’ muscles to burn fat for energy increased by around 35% after training. This was perhaps unsurprising as levels of the key signalling molecule called PGC-1α (see section 2) increased by 56%. What was even more impressive was that the levels of ‘glucose transporter protein’ (a protein that sits in muscle cell walls and allows muscle cells to soak up glucose from the bloodstream) increased by 260%. This helped increased overall insulin sensitivity in the subjects by 35%!
These results support findings from earlier studies. For example, a 2008 study on young women compared the metabolic benefits of high-intensity intervals performed three times per week for 15 weeks to the same frequency of steady state exercise(11). What the researchers found was that compared to the steady- state exercise, the intense intervals resulted in significantly larger reductions
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in total body fat, subcutaneous leg and trunk fat, and greater gains in insulin sensitivity. The researchers concluded therefore that high-intensity intervals may help to prevent type-2 diabetes.
Intervals are for everyone However, it’s not just unfit and/or overweight people that have been shown to gain health benefits by a period of interval training; studies have also been carried out on individuals with coronary artery disease and patients who have suffered a heart attack, patients with severe chronic obstructive pulmonary disease, individuals with metabolic syndrome, spinal-cord-injured individuals and those suffering with intermittent claudication (pain in the lower limb associated with atherosclerosis of the lower extremity arteries)(12).
In a comment article, McMasters University experts in the field of interval training for health concluded the following: “Although interval-type exercise training has been used by athletes for many years, the perception that it is unsafe and or unfeasible for less ‘fit’ populations is now being challenged by emerging evidence. Indeed, the body of accumulated evidence demonstrates that high- intensity interval training is a safe and valuable tool which can be used to combat many inactivity related disorders in a wide range of populations, and is no longer simply a training tool for the elite athlete.”
Compliance A final word on the health benefits of intervals. Previous studies have consistently demonstrated the beneficial physiological adaptations associated with exercise. However, for training to produce a substantial and significant impact on health, functional capacity and quality of life, any exercise programme has to be both adopted and then consistently adhered to. This is perhaps one of the biggest reasons why interval training is so effective for health.
In a 2009 study, a research team lead by Tjønna found that overweight adolescents, who performed three months of twice-weekly high-intensity exercise sessions, experienced reductions in several known cardiovascular risk factors to a much greater degree than those who received a more general multi-treatment strategy (diet, lifestyle counselling etc)(13). In fact, the superior effect of interval training was observed not just at the end of the three-month study period but up to eight months after the formal exercise training had been completed! Moreover, the authors also pointed out that ‘informal’ comments from the adolescents in the interval training group indicated that they were enthusiastic
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about the variation provided by the interval programme and were so encouraged by their own perceptions of increased fitness that they were motivated to continue interval exercise on their own after the 13-week experimental period!
One of the most appealing aspects of interval-type exercise is that it mimics the activity patterns that people typically experience in their activities of daily living – for example, climbing a flight of stairs. It may be therefore that this type of training translates into increased confidence and enthusiasm for similar challenges in daily life, thereby permitting greater gains in fitness and further improvements in health.
Summary Research shows incorporating relatively intense exercise into a training programme can provide valuable health benefits over and above steady- state training. Because interval training is an efficient and safe way of incorporating relatively intense bouts of exercise into a training programme, it is recommended for anybody seeking to maximise the health benefits of exercise!
References 1. Lancet. 1980;2:1207-10. 2. Lancet. 1973;1:333-9. 3. JAMA. 1995;273:1179-84 4. Prev Med. 2001;29:37-52 5. JAMA. 2002;288:1994-2000 6. JAMA. 1989;262:2395-2401 7. Obes Rev. 2003;4:101-14 8. Diabetes Care. 1996;19:341-9. 9. N Engl J Med. 1996;335:1357-62 10. Med Sci Sports Exerc. 2011; Oct;43(10):1849-56 11. International Journal of Obesity 2008; 32 (4): 684–91 12. Clinical Science 2009; 116, 315–316 13. Clin. Sci 2009; 116, 317–326
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Intervals: looking at the bigger picture
By the time you’ve read this far, you’ll hopefully be feeling impatient to get started on some interval training! But if you’re already training, you’ll need to know how to integrate some interval work into your existing programme. And if you’re new to training, there are some basic ground rules that you should follow before commencing with any interval programme.
Safety first – important! Before we go on to explore how to integrate interval training into an exercise programme, we need to discuss safety – particularly for those who are relatively new to vigorous training. By its very nature, interval training requires relatively intense efforts, which places a temporary, higher loading than usual on the cardiovascular system. It’s important therefore to understand the risks involved and how to minimise them to ensure safe and healthy training. Consider these two apparently conflicting truths:
1. The best way of lowering your risk of premature death is engage in regular vigorous exercise. 2. The risk of death during exercise is greater than the risk of death at rest.
How can they both be correct? Dr Paul Thompson, an eminent cardiologist, once said, ‘If your only goal is to survive the next hour of your life, you should get into bed – alone. But if your goal is to live a long, healthy life, then get some exercise for the next hour.’ In other words, while there is an increased risk of premature death during exercise compared to sitting around at rest, the health benefits produced by exercise are so massive that in the longer term, they hugely outweigh any small risk that occurs during exercise itself. Or to put it another way, the miniscule risk of death during exercise must be balanced against the massive risk of premature death conferred by a lifetime of inactivity.
So just how risky is exercise? In an effort to investigate the frequency of exercise- induced death, Dr. Thompson and colleagues collected data on all deaths during jogging in Rhode Island from 1975 to 1980(1). When victims with existing coronary artery disease were excluded, the annual death rate was estimated as 1 per every 15,240 previously healthy joggers. This figure is in agreement with
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a Seattle study where there was an estimated 1 death per year for every 18,000 physically active men(2).
The rarity of exercise-induced deaths does not justify complacency, however. Dr. Thompson also recommends that any person, whether young or old, who experiences any symptoms during exercise that might possibly be cardiac- related, should undergo a full cardiac evaluation prior to returning to training or competition. These symptoms include: ●●Chest pain or any other pain that could indicate a heart attack, including pain in the neck and jaw, pain travelling down the arm or pain between the shoulder blades ●●Feelings of ‘tightness’ or heaviness in the chest, arm, or below the breastbone ●●Extreme breathlessness unrelated to exercise intensity ●●A rapid or irregular heartbeat during exercise ●●Dizziness ●●Fainting ●●Nausea or vomiting
This cautious approach is not designed to deter you from starting interval training; merely that in matters of the heart, it’s always best to err on the side of caution. Those of you who are already performing regular, vigorous exercise can also take reassurance from the fact that the cumulative risk (during both active and inactive periods) for a fit and active person is dramatically reduced, compared with someone who is sedentary. This has been confirmed by surveys of studies examining the risks of a cardiac event during exercise testing. For sedentary persons, the risk of suffering a cardiac event during maximal or sub-maximal exercise is 4 in 10,000. However, studies on athletes appear to demonstrate the protective effects of exercise. For example, the German researchers Scherer and Kaltenbach found that in over a third of a million exercise tests carried out on athletes, not a single cardiac event occurred(3)!
Assessing risk Go and join any gym, and the first thing you’ll be asked to complete is a Physical Activity Readiness Questionnaire (or PARQ for short). Typical questions include whether you suffer chest pains, fainting or dizziness, breathlessness after mild exertion and so on. The main purpose of a PARQ is to identify those with any signs or symptoms of coronary heart disease, because the risks of a cardiac event during exercise are greatly increased when coronary heart disease is present. If you answer no to all of these questions, you’ll usually be cleared for exercise.
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However, while this approach is quick and easy to implement for instructors and trainers, PARQs only give a yes/no answer to whether someone can begin exercise and as such tend to lack subtlety. There’s no indication of the degree of risk that someone faces when they start exercise or up the intensity of exercise. Neither do they provide any recommendations about how any risk affects the way a person should commence an exercise program.
A more subtle, informative and flexible approach is to carry out what’s known as ‘risk stratification’ (in addition to a PARQ). This technique places you in 3 risk categories – low, medium and high – and is currently the preferred method of determining how an individual should begin exercising by the American College of Sports Medicine (ACSM). Risk stratification involves three steps: 1. Identify the risk factors that apply to you. 2. Calculate the risk category into which you fall. 3. Apply the exercise recommendations for that risk category.
At the end of this chapter, there’s a step-by-step guide on how to assess your own risk. If you’ve never undertaken any interval training before or have not been exercising vigorously in recent years, you are strongly recommended to assess your own risk to determine your risk category and whether you need to seek medical advice before commencing training (see appendix). Remember all the time, however, that the evidence is overwhelming – for long- term health and well being, vigorous exercise is simply the best there is!
Getting started If you’re relatively new to training and/or using intervals, you’ll probably be wondering how best to incorporate intervals into your training routine. Questions like “How many times per week?” and “Should I use intervals in addition to or instead of my normal routine”? are commonly asked by those new to intervals. One thing that’s important to understand is that any interval training you perform has to be seen in the context of your overall training programme, rather than in isolation.
Without doubt, the biggest risk for those who are already training and who want to add intervals to their programme is overtraining and/or injury. That’s because intervals, by their very nature, are relatively high intensity and high- intensity training imposes a higher loading on the body, even when that higher- intensity training is only of short duration. So for example, supposing you want
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to increase running fitness and are already running 3 times per week. Adding an extra session in the form of intervals will certainly help running fitness. However, the increased training load will require increased recovery while at the same time, you’ll have less time for recovery and that’s a potential problem.
Overtraining Building maximum fitness is like walking a tightrope; one the one hand, you need to load the body with enough training stimulus to produce the training adaptations and fitness gains you want. On the other hand, you need to allow the body enough time to recover in between training sessions – it is after all during recovery that this adaptation occurs. If you don’t allow enough recovery after a session, you are likely to feel tired and even perhaps sore when you next train. Not the end of the world perhaps, but it could mean that the next session is lower quality than you had intended. A much more serious problem however is when there’s insufficient recovery over a period of many sessions lasting weeks or months. Not only does this increase the risk of injury, it can also lead to ‘overtraining syndrome’, which is characterised by a number of symptoms including: ●●Feeling washed-out feeling, tired, drained, lack of energy ●●Mild leg soreness, general aches and pains ●●Pain in muscles and joints ●●A noticeable drop in performance ●●Insomnia ●●Headaches ●●Lowered immunity – evidenced by an increased number of coughs, colds and sore throats ●●A decrease in your desire and ability to train either long or intensely ●●Moodiness and irritability and even depression ●●Loss of enthusiasm for the sport ●●Decreased appetite
A full discussion of overtraining is beyond the scope of this report but suffice to say it’s something that you will definitely wish to avoid! Fortunately, there are some simple ways of monitoring your recovery to ensure you don’t inadvertently slip into an overtrained state (see box 1).
Guiding principles Okay, let’s look at the nitty-gritty of incorporating intervals into your training programme. We can make a number of practical recommendations using two key guiding principles. Firstly, it’s essential to allow sufficient recovery when
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Box 1: Monitoring recovery Interval training is an extremely efficient way of building fitness. However, the relatively intense nature of the training can impose a significant extra loading on your body, which demands sufficient recovery. Fortunately, there are some simple checks you can carry out to monitor your recovery and look for any early signs that you might need to back off a bit in terms of training volume, training intensity or both. ●●Record your resting heart rate (in beats per minute – bpm) each morning before you get out of bed. You should find that it is fairly constant from day to day. However, if you record any marked increase from the norm, this may indicate that you aren’t fully recovered. ●●Use a heart rate monitor to record your heart rate bpm during a steady state session at a specific speed or power output. In the short-term, it should remain fairly constant and in the longer term (as your fitness improves), your heart rate should drop. If you notice an increase at any time, this may indicate that you are not getting adequate rest and recovery. ●●Another way to monitor recovery to use something called the ‘orthostatic heart rate test’. To perform this, lie down and rest comfortably for 10 minutes the same time each day (morning is best). At the end of 10 minutes, record your heart rate bpm. Then stand up and after 15 seconds, take a second heart rate in beats per minute. After 90 seconds, take a third heart rate in beats per minute and then after 120 seconds, take a fourth heart rate in beats per minute. If you’re well rested, you will have a consistent heart rate between measurements. However, a marked increase (10 beats per minute or more) in the 120 second-post-standing measurement indicates that you have not recovered from previous workouts and that it may be helpful to reduce training or rest an extra day or two before performing another workout. ●●Finally, a technique known as ‘heart rate variability’ (HRV) can be extremely useful. HRV relies on the fact that in a well-recovered person at rest, there’s quite a bit of natural variability in the time interval between each heart beat. However, when recovery is insufficient and fatigue sets in, that natural variability is diminished. Fortunately, modern technology now means that some heart rate monitors can record your HRV and alert you when your recovery is not up to scratch! adding intervals to a programme – for example by reducing the training load elsewhere. Failure to do so could result in an increased risk of overtraining and/ or injury. Secondly, because interval training is fairly intense, it’s important to structure your routine so that you are fresh before your session(s) of intervals. If you’re not fresh beforehand, you might be tempted to skip the intervals or if you do them, find them too tiring to complete. Let’s see how these work in practice:
For those new to intervals 1. If you’re new to intervals, you should start by adding no more than one interval session per week and cutting back on an existing non-specific workout elsewhere. For example, if you’re training to complete your first half-marathon
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by building up the mileage on one long run each week, you wouldn’t replace that workout with intervals, but instead replace a less specific session. 2. Be gentle on yourself – start easy and work your way into your sessions. For example, instead of aiming for 10 x 1 minutes at 90% of maximum effort from the outset, start with 4 or 5 intervals at 80% effort. Gradually build the number of intervals then build the effort level to 90% 3. Try to ensure that you schedule a rest day after your interval session, or at the very least, a day where any training load is very light. 4. Ensure you go into your interval session fresh by scheduling a rest day (or a very light training day) the day before. Never do intervals tired. 5. Once your body has adjusted to performing intervals and you are finding them more manageable, you can add back in the training session that you initially removed. However, you must still ensure you continue apply principles 3 and 4 above. 6. Remember that quality is king; rather than try and add a second interval session too soon and becoming fatigued, aim to ensure that you concentrate on performing a really high-quality interval session once a week. 7. Monitor your recovery. If you feel you are becoming fatigued, take a week off from intervals completely. 8. Complete beginners to exercise should avoid high-intensity intervals completely until they have built some base aerobic fitness.
For those accustomed to interval training 1. Aim for one or two interval sessions per week. However, ensure you adhere to principles 3 and 4 in the section above and space the two sessions as far apart as possible. 2. If you are performing two sessions per week, try two different interval sessions to prevent boredom while bearing in mind your overall goals (eg targeting the relevant energy systems in your particular sport/event). 3. Use a training diary so you can gauge how different interval sessions work for you – eg easily spot positive (or negative) changes in performance 2-3 weeks down the line as a result of implementing a particular type of interval session. 4. If you strength train, try to ensure that you keep your resistance sessions as far apart from your intervals as possible (to help ensure maximum recovery). For example, if you’re interval training on a Monday and Thursday, you should resistance train on the Saturday. 5. Try periodising your interval sessions. So for example, you could perform two weeks of 2 sessions per week followed by two weeks of 1 session per week. Or you can block periodise – eg perform intervals two or even three times per
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week for four weeks then have a complete break for four weeks. The key point is that by varying total workload, you allow your body periods where recovery and adaptation can take place. 6. Never perform interval sessions into the run up to a race or match. You’ll just end up sapping your race-day performance. 7. Always monitor your recovery and check for signs of overtraining when undergoing an extended period of interval training, especially if you are also performing a high load of steady-state training (eg distance cycling, triathlon, rowing etc).
References 1. JAMA. 1982;247:2535-8. 2. N Engl J Med. 1984;311:874-877 3. Eur Heart J. 1982 Jun;3(3):199-202
Appendix: How to assess your risk Work through the following steps to assess your risk and readiness to start interval training:
Score +1 if it applies to you, Positive Risk Factors otherwise 0
Family history of heart disease. Do/did you have a father, brother or son, who suffered a heart attack or sudden death before they reached the age of 55 years, OR Do/did you have a mother, daughter or sister, who suffered a heart attack or sudden death before they reached the age of 65 years?
Smoking – Do you smoke, or have you given up smoking in the past 6 months?
Blood Pressure – Has your blood pressure recently been measured at over 140mm (systolic) OR 90mm (diastolic) on more than one occasion?
Cholesterol – Do you have a total blood cholesterol level of over 5.2mmol/L OR an HDL cholesterol level of less than0.9mmol/L OR are you on cholesterol lowering medication?
Obesity – Do you have a waist girth of more than 100cms (39 ½ inches) OR is your BMI (that’s your weight in kilos divided by your height in metres squared [kg/ m2]) over 30? Blood Glucose – Has your fasting blood glucose been measured at more than 6.1mmol/L on more than one occasion? Activity – Are you currently inactive?
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Add up your score and then answer the final question about HDL cholesterol below. High levels of HDL are known to be a negative risk factor because they reduce the risk of coronary heart disease (CHD). So if you answer yes to this question, you score –1 (ie you can knock off a point from your score above):
Score minus – 1 if it applies to Negative Risk Factor you, otherwise 0
Is your HDL cholesterol level above 1.6mmol/L?
Tot up your points and you’re now ready to assess your risk. If you’re male and under 45, or female and under 55, look at the table below:
Risk (males<45; Points Score females <55)
1, 0 or 1 point Low
2 or more points Moderate
Any of the symptoms listed below regardless of points: High Known heart condition/heart murmur Breathlessness after gentle exertion Chest pains Fainting or dizziness Swollen ankles Palpitations or tachycardia (rapid heart beat) Pain/pressure in chest, left side of neck, shoulder or arm during or shortly after exercise Intermittent pain or discomfort in the calf muscle during or after exercise
If you’re male and 45 or over, or female and 55 or over, you need to look at the table below (The reason for the differences between the two age groups is that age itself is a risk factor for CHD):
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Risk (males>45; Points Score females>55)
-1, 0 or 1 point Moderate
2 or more points Moderate
Any of the symptoms listed below regardless of points: High Known heart condition/heart murmur Breathlessness after gentle exertion Chest pains Fainting or dizziness Swollen ankles Palpitations or tachycardia (rapid heart beat) Pain/pressure in chest, left side of neck, shoulder or arm during or shortly after exercise Intermittent pain or discomfort in the calf muscle during or after exercise
Using your risk stratification The terms ‘low risk’, ‘moderate risk’ and ‘high risk’ are only relative terms, so if for example your risk analysis suggests you’re in the medium risk band, it doesn’t mean that there’s a moderate risk that you’ll suffer some kind of coronary distress during exercise! All it means is that you are a greater risk compared to a low-risk individual and therefore need to take things more gently when you commence your exercise program. The ACSM has guidelines on whether or not different risk groups require a medical examination before beginning exercise of different intensities and these can make a good starting point for determining how to proceed:
Exercise Intensity/Risk level Low Risk Moderate Risk High Risk Gentle-Moderate Exercise No medical No medical Medical clearance (ie 40-60% of VO2 max or 40- clearance required clearance required is required 60% of heart rate reserve) Vigorous Exercise No medical Medical clearance Medical clearance (ie above 60% of VO2 max or clearance required is required is required above 60% of heart rate reserve)
If your risk is classified as ‘moderate’ or ‘high’, you should consult your GP before commencing vigorous exercise such as interval training (just to be on the safe side).
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Interval Training Workouts
In the final section of this report, John Shepherd provides a range of sample interval workouts, which can be used across a wide range of sports and ability levels
Whether you are a sprinter or a marathon runner (or anything in between or beyond), you need to use intervals. Likewise if you are a games player then you need to incorporate interval training methods into your preparation – for footballers, rugby players and tennis players, for example it’s a must. The good news is that there are numerous ways that intervals can be worked into your training programmes, making them very specific to your sport. Interval training also provides benefits for fitness enthusiasts; you can use them to get fit (when long, sustained efforts would not be possible) and to boost your fat burning and calorie burn, when you have reached an intermediate/advanced level of fitness. All these and other interval training methods are explained and illustrated in the following sections of this chapter: ●●Section 1: Interval Training for Endurance ●●Section 2: Interval Training and Sports Performance ●●Section 3: Interval Training for Speed ●●Section 4: Interval Training for Fitness ●●Section 5: Interval Training and Resistance Training
Section 1: Interval training for endurance
Triathletes, middle, long and ultra-distance runners, rowers and cyclists all need to interval train. Building a base of fitness through LSD (long, slow, distance) running is a key component, as it will build a lasting physiological foundation for endurance specific adaptation. However, interval training cannot be neglected. Many endurance athletes use faster-paced anaerobic intervals at over race pace as part of their tapering training phases, but it’s crucial to consider how intervals at race pace can play a very significant role in boosting endurance, assisting base building and lifting the ability on the part of the athlete to sustain longer and longer periods of work at race pace and beyond.
Boosting your race pace If you are serious about your endurance training then you will have target paces for your workouts and ultimately your race-event. To run a 2 hour 20 marathon you will need to complete each mile in 5min 19sec. Thus a great way to ‘learn’ how to achieve that pace would be to run intervals at that pace, staying within
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a designated heart rate zone/percentage of your V02max. You would – having worked out your training threshold – run a designated number of intervals at this pace, in order to progressively lift your ability to run consistently at this pace. These intervals could start at 15min in duration and progress to 30min, with 3-4 intervals being run, depending on your fitness and the stage of your running preparation. Or you could include a 30-50min section at this pace during your regular longer runs of, (such long runs, are carried out mainly at weekends, by most serious non-elite marathon runners and are a staple ingredient of marathon preparation).
This race pace principle works for all running distances – obviously the race pace will be slower and less intense for long races and the reverse for shorter ones.
Here are some further examples of race paces for 10k running and marathons:
Table 1: Selected running distance events and race paces Distance Time/pace Time/pace Time /pace Time /pace
10k 31.04/5.00 37.16min/6.00 43.29min/7.00 49.42/8.00
Marathon 2.28hrs/5.39 2.54hrs/6.39 3.11hrs/7.19 3.55hrs/8.59 Paces are per mile. Adapted from: www.coolrunning.com Go to this website to calculate your splits times for various race distances and splits.
Training at your anaerobic/lactate threshold For most (long) endurance events you will want to maintain a pace that does not tax your anaerobic system too much. The longer the race, the more important this becomes. If you start to run/row/cycle above your threshold you will be mainly utilising your anaerobic system, which only has a finite amount of energy to release. If you were to try to sprint for as long as you could, you wouldn’t be able to last for more than 90 seconds. The longer a race is, the greater the aerobic element and the lower the anaerobic one. A marathon, for example, is 95% aerobic and 5% anaerobic. So it’s all about developing and eking out your aerobic energy.
By training at an intensity below your anaerobic/lactate threshold, you will gradually develop your body’s ability to burn fat and preserve your body’s more limited carbohydrate stores (training above race pace and targeting your anaerobic system through intervals is covered later). Being able to do your base building at what’s also known as fat max is another key to successful endurance
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Intervals for lactate threshold As previously mentioned, interval training is a great way to boost lactate threshold. Boosting lactate threshold simply requires running/cycling etc at your maximum aerobic pace. Here are some sample lactate threshold boosting interval workouts (you will need to know your maximum heart rate to complete these sessions.
●●3-6 x 4min at 85% heart rate max – recovery 1-4 min depending on your fitness ●●2-3 x 10min at 80% heart rate max – recovery 2-3min depending on your fitness Note these workouts do not require you to run anaerobically hard. Expect mild discomfort at the end of each interval. Threshold run – this is not strictly speaking an interval session as it is a one-off effort, but it is a key workout. To complete this workout work at a pace that ‘stops’ you between 15-20min – ie at a point when you are near to maximum heart rate. The higher your lactate threshold the faster you will be able to complete race pace at and the quicker you will be able to recover, after more intense intervals and after surges in races, for example.
training (going into detail about this is beyond the scope of this section, but in trained endurance athletes it’s around 80% of heart rate max and they will do the majority of their base-building at this level).
However, from an interval training perspective you can also boost your endurance by training at /anerobic/lactate threshold. The fitter you get the longer you will be able to maintain this maximal aerobic pace before you surpass your threshold. This type of training will boost your aerobic performance and elevate your race pace – these are a consequence of changes in your body’s endurance physiology. As with all prolonged endurance training (aerobic and anaerobic) you will increase the stroke volume and the rate of work being done by your heart (heart rate will lower) and your muscles will become more efficient at sustaining the chemical reactions needed to continue to power your endurance engine. Specifically in this case you’ll develop more oxygen carrying capillaries in your muscles and mitochondria (the power plants that convert chemical energy into mechanical energy).
High-intensity interval training Tabata training is a form of High-Intensity Interval Training (HIIT) as discussed earlier in this report. Dr Izumi Tabata discovered that very short super- maximal intervals (in terms of heart rate and V02max) boosted all markers of
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endurance potential, for example, lactate threshold, V02max, race pace and endurance economy (the ability to complete an endurance activity at a fast, but relatively comfortable pace). Tabata intervals – unlike the interval workouts provided previously – will take you well into your anaerobic ‘red’ zone. Very intense Tabata workouts are very tough and should not be performed by the unconditioned.
Examples:
●●4-10 x 20sec of near maximal effort followed by 20sec rest ●●After a 3min warm up, complete 60sec of work at 95% V02max then recover for 75sec and repeat this cycle 8-12 times (using this protocol, Tabata found that the gains were very similar to those who trained using steady-state methods 5 times a week) ●●8 x 20sec at 170% V02max with 10sec recovery
The benefits of in particular intense Tabata workouts are to be found in terms of relatively quickly boosting anaerobic ability, strength and power and exercise (aka pain!) tolerance.
Numerous endurance experts (eg running guru Tim Noakes) are convinced that an athlete’s ability to combat pain when completing endurance activity is crucial to lifting their ability and to becoming champions. HIIT is a great way to achieve this. More examples of HIIT will be provided in the following sections.
Section 2 Interval Training and Sports Performance
There are numerous ways that interval training can be used within sports conditioning. Obviously, the methods presented in the previous section can be utilised where relevant. However, specificity rules in the world of contemporary sports conditioning; although it will benefit a footballer, for example, to be able to complete a high intensity Tabata session on an exercise bike, in terms of general physical preparedness there are much more relevant ways of doing this. In this section you will find a number of sport-specific interval-based sessions examples that you can adapt for your particular sport.
Football Football is a fast stop-start sport with players required to make runs at various paces, in various directions, when fatigued whilst completing various complex
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skills. Physically and mentally fatigued players can lose a ‘yard’ and in the worst cases scenarios the match, and also sustain an injury.
Modern football conditioning is light years ahead of the days when pre-season consisted of 5k runs. Now, much match fitness training revolves around small-sided games, played by 6-8 players on a contained (smaller) pitch, with multiple balls being available. Multiple balls are used so that a ball can very quickly be returned to play after the one being used has gone out of play. Rather like a runner’s interval workout, the protocols of the session and therefore the outcomes of the session can be manipulated for different training effects. You’ll find below examples of these types of workouts and others (note see also sections 3, 4 and 5 for more relevant workouts).
Football Interval Sessions ●●Session 1: 8 vs. 8 on smaller pitch with multiple balls – high tempo then 4 x 3min with 2min jog recovery; ●●Session 2: 8vs. 8 on smaller pitch with multiple balls – medium tempo then 5 x 5min with 1 min jog recovery ●●Session 3: 8 vs. 8 on smaller pitch with multiple balls – v high tempo then 10 x 1 min with 1 min jog recovery
Individual/small player number football interval workouts 1. Pass repeats and 20m out and back run: Two players stand about 4m apart and perform a series of 20 side-foot alternate passes back and forth. The designated player on completion of the twentieth pass, turns, and runs 20m round a cone and back to his starting position to repeat the drill. On completion of the twentieth pass he or his colleague makes the 20m out and back run. The number and speed of the runs can be varied as can the number of passes.
2. Shuttle/speed ladder runs: Shuttle runs are a staple of football training and with the introduction of speed ladders these types of agility sessions become much more specific to football. a) Players run through speed ladder one foot at a time and run 30m x 6 with walk-back recovery; b) Players side-step through speed ladder to left and then turn, and side-step to their right in a ladder placed parallel. This can be done in pairs (or others numbers of players) with the time taken for the other player (or players) to complete the task as recovery. A running section can also be added before
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the completion of the ladders run, for example a 20m sprint with walk back recovery. The recovery could be based on the number of players performing the drill or on a designated time on time off basis.
Football Fartlek interval session Fartlek is Swedish for speed-play and it’s a method of training used by middle and endurance runners. For example, during a 30 minute effort (normally performed on grass), the runner will run various distances at various speeds as he feels fit. He might run a 300m rep at 60% effort, then jog very slowly for 2 minutes before repeating. He then may do some shorter 100m runs at 80% effort with a 50m jog recovery. The number and intensity of the reps in a true fartlek are delivered on the basis of how the runner feels (unless he is part of a group when other runners may lead certain segments or take it in turns to do so). From this description it should be readily seen that this type of interval workout would ideally suit a footballer, particularly in pre-season, when match fitness is being sought.
Example of football fartlek session: Player: striker Duration: 15 minutes Efforts to include: jogging, walking, sprints over 5, 10, 15 and 20m. These can be practised using different types of starts – eg walking, jogging, faster running and standing still. Recoveries can be walks, jogging or faster. Durations in the football fartlek could last for a single repetition, a designated number of repeats or time. Bear in mind that the efforts of all footballers are primarily anaerobic. These types of workouts will boost all markers of the endurance fitness needed for footballers – ie improve lactate threshold, V02 max and aerobic ability. This is in very much the same way as the Tabata workouts described in section 1.
The technological football revolution Such is the array of technology now available in elite football that players’ running speed and distances can be meticulously recorded and monitored by systems (such as ‘Pro-zone’). Using the information recorded, carefully constructed interval training sessions can be designed, which reflect the needs of players and their respective positions. These could also include the nature of the movement patterns required by the players and the typical recoveries and types of recoveries they get in a match.
Centre forwards will often do a lot of work with their back to the opposing team’s
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goal and will make more turns, whilst wing backs will have to make long forging runs up the pitch of 50 plus yards and then get quickly back into position. Mid- fielders are famed for longer and harder sustained levels of effort. For example, in a recent (2012) match against Burnley, Derby’s Craig Bryson ran 2.37kms at very high intensity, whilst completing a total of 13km during the match! Armed with this knowledge and more, football conditioning (and match play, in terms of substitutions for example) can become very systematic. Arsene Wenger, for example – one of the pioneers of sports science based football – used to substitute Dennis Bergkamp around the 70th minute as he knew the striker’s pace would drop off significantly.
The right interval training can make you a much better player but you also have to understand your playing position’s requirements and monitor your performance. Okay, you might not have access to Pro-zone but you can make some very educated decisions vis-a-vis the type of workouts you should be performing to reach your best match fitness levels. Hopefully the sample workouts provided in this section will provide you with the knowledge to do so.
Section 3 Interval Training for Speed
In this section we take a look at how interval training can boost your top-end speed, and specifically your out and out sprint speed. The workouts in the previous two sections can help develop this – eg the football fartlek session (see section 2), which includes sprints – and it could be argued that race pace work (see section 1) will also provide the ‘right’ optimum speed for a marathon runner to optimise their performance. However, these two types of interval-training induced speed utilise a higher percentage of the aerobic energy system than those that we are concerned with in this section.
Here we focus on what are known as the immediate and short-term anaerobic energy systems. The former supplies explosive energy for up to 8 seconds and the latter for up to 90 seconds. They rely predominantly on stored muscle energy sources and have much less reliance on oxygen transported by the heart and lungs. They also target your ‘fast twitch’ speed, and power-producing muscle fibres. The sprint interval workout examples provided are designed to make you a faster runner and improve speed for running distances up to 200-400m. To run at speed for longer you would need to run slower reps and tax your short-term anaerobic and aerobic systems to much greater extent.
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Sample Sprint Workouts Goal to improve 0-40m speed – ie acceleration 1. 6 x 20m sprints from standing/leaning start (90sec recovery between efforts). 2. 4 x 10m; 2 x 20m; 2 x 30m; 1 x 40m from standing/leaning start (60sec recovery between 10m runs, then 2min before 20m runs with 90sec between each, then 2min before 30m run with 2min between each and then 3min before the 40m run). 3. 6 x 40m runs with 10m jog approach (4min recovery between each effort). 4. 20m/30/m/40m/50m/40m/30m/20m from standing/leaning start (recovery, 60sec/90sec/2min/2min/2min/2min/2min/90sec. The recoveries are uneven on the down the clock element of this session to counter accumulating fatigue). 5. 2 x 3 x 60m sprints from standing/leaning – with 3-4min recovery between each and 5min between sets.
The aim of all these sessions is to run flat out – fatigue caused by too short an interval must not affect performance. If you do feel yourself losing speed then terminate the session or reduce the running distance or increase your recovery period.
Short-term anaerobic system speed workouts These interval workouts require you to run at over 80% of your flat-out speed for longer than the previous ones. They are high-intensity speed runs. You must run relaxed and fluently, with fatigue only having a minimal effect. 1. 2 x 3 x 120m at 80% effort (4min recovery between runs and 10min between sets) 2. 80/100/120/140/120/100/80m runs at 85%-90% effort (take as much recovery between runs so that you can maintain the speed required. A slightly easier variation of this session is found below). 3. 140; 120; 100; 80; 60 – perform these runs at 90% plus speed. Using a jog start to the start will reduce the energy needed to accelerate and ease the energy demands of the runs (recovery as much as you need to maintain speed and fluency). 4. 2 x 180m 95% effort – this workout will tax those who are unconditioned because this distance drains the short term anaerobic system. Performing some of the above workouts 2-3 times a week will prepare you for taking on these efforts (recovery should be complete, therefore 15-20min between runs. For those who are specifically conditioned these runs can be performed at 100% effort).
400m running type speed interval training As indicated this type of running relies on the short-term anaerobic and aerobic
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systems to a much greater extent than the workouts above. The workouts required will produce considerable lactic acid accumulation (a by-product of tough exercise). The idea when developing 400m-style endurance is to be able to create conditions in your muscles that restrict the debilitating effects of lactic acid. These workouts are therefore not for the unconditioned and nor are they really suitable for those using interval training to improve their top speed (these workouts have been provided previously).
1. 3-6 x 300m with 60sec recovery – run at 80% effort. 2. 6 x 200m run at 85-90% effort with 45sec recovery (your speed will slow but it’s the effort that counts as you have to run under the conditions of ebbing and flowing lactic acid build up) These interval workouts will really boost your muscles’ lactic acid tolerance. 3. 400m at 90% effort 30 seconds of rest then go again. This is a killer workout! It will be impossible to complete the second 400m at anywhere near the pace of the first. It’s more of a mental toughness run. However, your muscles will quickly adapt. These workouts should be used sparingly and not before any important competitions (should you be a competitive runner). You must be rested before completing them and have an easy session or two in the days after. 5. 6-10 x 40m sprints with a turn-around recovery. This is an equally tough workout. Simply (!) sprint 40m slow, immediately turn, walk about to where you finished the 40m and repeat. You’ll have only a few seconds recovery and each run will become a battle against accumulating lactic acid.
Timed duration intervals Michael Johnson (world 400m record holder) and his coach Clyde Hart used to include workouts that required the athlete to run reps for a designated time at a designated pace – usually expressed as a percentage of maximum speed.
A 38-second run would take an athlete of Johnson’s class to 300m and beyond. As the athlete got fitter and quicker, the distances achieved in those 38 seconds would increase. Why run intervals like this? The idea is that you run to a point where fatigue – although it has begun to set in – has not significantly altered running mechanics. Thus through repetition of these duration type interval workouts, the athlete learns to run further, faster and fluently across the conditioning period. There is an avoidance of trying to make distances in certain times when the athlete could push that bit too hard. Rather, pace and fitness improve commensurately with the key to running fast – speed.
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Mixed-speed interval workouts It is also possible to combine different speeds of running within a workout. An innovative way to do this for developing speed-endurance is to mix short explosive efforts with longer, sustained high-speed runs. The recovery should be sufficient to allow the athlete to run at or close to the required pace. Example: 2 x 30; 2 x 120m; 1 x 60m, 1 x 150m, 1x 40m, 1 x 200m (recoveries sufficient to complete each effort at 90%).
This is an unusual workout that many track athletes will not even have used. It does throw anaerobic (immediate and short-term) energy system usage around and will also have an effect on the central nervous system. Consequentially these workouts must be used circumspectly in a training programme.
S ection 4 Interval Training for Fitness
For the fitness trainer, beginner or advanced, interval training opens up a realm of possibilities. It can be used to develop fledgling fitness or boost those who have already reached a high level.
Interval training for developing fitness Most people when they start a fitness training programme will often use aerobic methods to burn fat and lose body weight. This method, although effective, particularly at the start of a fitness programme, has its limitations. There are potentially better ways to shape up, tone up and slim down. Resistance exercises, for example, can have a very significant effect in this respect. It is beyond the scope of this report to go into a detailed explanation. However, it should be noted that lean muscle tissue is a very effective all day and everyday calorie burner and using interval training methods can create a significant calorie burn (section 5 looks at resistance based interval training methods specifically). Additionally and pertinently to the subject matter of this report, it’s very possible that a beginner would not be able to sustain a run or a row for a significant period of time necessary to create a significant calorie burn and fitness effect. And this is where low-intensity interval training comes in; a longer work period can be established by dividing up periods of effort with rest periods. The session as a whole will still be of a low intensity and be within the aerobic zone.
Sample ‘developing fitness’ interval training workouts 1. Running on treadmill. Walk for 5min to warm up. Run easy for 1min. Walk for 2min at brisk pace and slight incline 2-4%. Run for 1min, Repeat for 3 more
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A Note on Short to Long approaches to Interval Training What’s the thinking behind the above type of interval workout? Speed! Or more specifically speed coupled with speed-endurance with the goal (when incorporated into a relevant training programme from the start of the training year) of building endurance on speed. This leans on what’s known as the ‘short to long approach’ to speed development, rather than a ‘long to short’.
The latter method is perhaps the more traditional philosophy. Here athletes perform long intervals at slower paces, with the paces and number of reps increasing throughout the training period. This builds speed upon endurance. The possible problem here is that the athlete loses their speed in the early stages of training, when running more slowly and then works to get it back.
With the short to long approach the idea is that greater speeds will be achieved throughout the training programme and ultimately when it matters (ie competitively) but with similar levels of endurance that would be gained using the long to short approach. Thus the short to long athlete will be a better athlete as they are able to complete their runs faster. Note: not all athletes/ trainers will respond in the same way, so if you are going to try to base your interval training on an approach do be prepared to experiment.
cycles (not including warm-up). Warm down with very slow 5min walk. This way the novice exerciser would get a total of 26 minutes of exercise. If they tried to run this continuously it is very unlikely that they would not have been unable to complete the distance. Here a progression for the workout: increase the periods of running and walking by 30 seconds a time, keeping the recoveries the same, then when the run intervals are 3 minutes long, move onto 5-minute intervals with 2-minute walk recoveries and begin to increase the run and intervals by 30 seconds as before up to 8 minutes. This workout would then last for 50 minutes. 2. Rowing. Row for 3min at 20-22 strokes per min. Row for 1min, 24-26 strokes per min. Row for 1min 20-22 strokes per min. Repeat for 3-6 reps. If using a Concept2 rowing machine, set the resistance at 4-6 on the fan and make sure you learn how to row efficiently (your legs should supply the majority of the power, with your arms finishing off the stroke).
Sample interval training workouts for those of an advanced level of fitness Obviously, many of the examples from the interval training for endurance and speed sections could be used for advanced fitness developing purposes, such as Tabata training and speed endurance running intervals. As a fitness enthusiast you will be concerned with developing improved all-round physical condition, burning calories and shaping up. Your training should be specific but not as
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one-dimensional as a sports performer following a sports training programme. Your overall approach should reflect a cross training one – involving elements of resistance and CV (aerobic and anaerobic work). Here are some workout examples:
Pyramid interval rowing machine session (Develops high-end aerobic fitness, pushing up lactate threshold and V02max) Warm up then perform the following (SPM = rowing machine strokes per minute): ●●5min at 20-22 SPM ●●4min at 22-24 SPM ●●3min at 24-26 SPM ●●2min at 26-28 SPM ●●1min at 26-30 SPM ●●2min at 26-28 SPM ●●3min at 24-26 SPM ●●4min at 22-24 SPM ●●5min at 20-22 SPM
Note there is no recovery between the intervals as you switch up and down in terms of strokes per minute. Once you get familiar with this session you should be able to match your SPM with either power outputs per stroke and/or speed per 500m. As your fitness improves, these will improve at the given SPMs.
This session requires you to be a proficient rower. Each interval builds on the prior one in terms of stroke speed; however, you are in control of each interval and should not be working flat out. This workout should take you into anaerobic territory as you ascend the pyramid and then out of it and back into aerobic territory as you descend it.
Exercise bike power intervals (Develops leg power, V02max and lactate threshold) Warm up then 2min at 80RPM (revolutions per minute) on a light to medium resistance followed by 10sec flat out at heavy resistance. Repeat 8-10 times.
Despite looking easy – this workout is not! Cycling flat out for 10 seconds against a heavy resistance is tough, and after the second or third interval, that 10 seconds will be feeling like 30! It’s important that you use a 2-minute recovery as we are looking for near maximal power outputs. Unlike the Tabata workouts in the interval training for endurance section this interval workout does not want to suffer from
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significant reduced power outputs and slowing – so use those recoveries.
Anaerobic rowing machine intervals Warm up then 10 x 1min at 90-100% effort with 90sec easy rowing recovery (or complete rest if new to rowing).
This session will tax your powers of err power production, lactate tolerance and willpower. Your SPM will be in the high 30’s and as the 1-minute intervals progress, hanging on for those last few seconds will become more difficult. Those new to this workout should begin with 4-6 intervals and must have mastered rowing technique as poor technique could lead to injury.
Longer intervals for building a base of fitness Longer intervals in excess of 5 minutes can be used to improve your exercise economy and your aerobic/anaerobic fitness and calorie burning. For example, using a treadmill (heart rate controlled) perform 3 x 8min with 2min walking recovery. Run each interval with a heart rate of 80-85% maximum. Keep within this upper limit to improve your running economy, this will mean dropping your pace as your heart rate elevates (unless you are super fit, that is!). This principle can also be used in other activities (rowing, cycling etc).
Section 5 Interval Training and Resistance Training
It’s probably not fully appreciated how interval training can be applied to resistance training. However, periods of work interspersed with periods of recovery form the basis of all resistance sessions. In this section we take a look at forms of resistance training that have a particular interval training foundation in which they develop CV fitness (and not just muscular strength or endurance).
Lower body/upper body supersets Supersets simply combine one or more exercises into a set of exercises, which are performed one after the other. Lower body/upper body supersets are a very useful tool for those looking to add a cardiovascular element to their resistance training or increase the calorific demands of their workout. Hence this form of superset has a particularly relevant interval training nuance. Simply perform a lower body exercise of your choice and immediately follow it with an upper body exercise. Rest for 30-60 seconds before repeating. Always perform the lower body exercise first as they tend to elevate the heart rate the most, making the method more effective.
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Peripheral heart action training (PHA) Looking for a do-it-all workout that strengthens muscles, improves fitness and burns a whole load of calories? Look no further than PHA training. PHA covers and develops all aspects of fitness. When we exercise, oxygen carrying blood is diverted to the working muscles preferentially. This ‘shunting’ of blood requires an increase in workload by the cardiovascular system (the heart and lungs). If, as in PHA training, we then immediately perform an exercise for a different muscle group, oxygenated blood has to be pumped to the new area of the body and the CV system again bears the brunt of the work. By strategically selecting muscle groups that are anatomically far apart (or peripheral), the heart and lungs have to work hard, even though the body is not performing conventional cardiovascular exercise.
Here is a template into which you can slot your favourite exercises. Note that the exercises should be what are known as ‘compound’ meaning that they utilise more than one joint. The greater the number of joints and muscles involved, the more effective the workout.
●●Any cardio for 5 minutes ●●Leg exercise ●●Upper body pushing exercise ●●Leg exercise ●●Upper body pulling exercise ●●Any cardio for 5 minutes
Example PHA workout 1: Skip for 5 minutes Squats Press-ups Repeat resistance exercises for 2 laps Lunges Chin-ups Jog for 5 minutes
Example PHA workout 2: Step-ups for 5 minutes Supine hip bridge Handstand press-ups Repeat resistance exercises for 2 laps Squat jumps Body rows Jog 5 minutes
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Each workout is a ‘stand alone’ routine but could be combined into a single workout (although not for the faint-hearted)!
When selecting repetition ranges, stick with moderate to high reps (12 – 20) as this will provide the greatest challenge to the cardiovascular system. Don’t be surprised if the residual fatigue caused by the extra demands of PHA training requires you to reduce your working weights compared to when you perform the same exercises in a more traditional manner. Being out of breath can make even the simplest exercise more challenging!
To round off your PHA workout, feel free to add in any arm isolation or core work you feel is appropriate but only after you have completed the main PHA segment. Remember, though, although not trained directly, both the muscles of the arms and the core have been exposed to a fair amount of work so their inclusion is not essential if time is an issue for you.
Escalating density training – using very short intervals between exercises EDT is a training system that was developed by Charles Staley, a famous fitness trainer from America. According to Staley, the counting of sets, reps and rest intervals detracts from the main principle of exercise – overload. Staley’s system of EDT eliminates these concepts and focuses on one factor – how much work is being done.
EDT requires the pairing of two dissimilar exercises and the use of a stop watch. The exercises are performed in a loose back-to-back style for a pre-determined duration (called a PR or Personal Record Zone). Rest periods are intuitive and the exercises are repeated as many times as possible in the allotted PR zone – eg 15 minutes. At the end of the PR zone, the reps for each exercise are totted up and recorded. The next time this workout is performed the idea is, and using the same loads as before, to complete more repetitions in the same time frame. More work completed? The density of the workout has increased and therefore overload has been achieved. When you can do 20% more repetitions than your first attempt, it’s time to increase the weights you lift by selecting more demanding versions of your exercises.
When performing an EDT workout, it’s important not to overstretch yourself in the first few minutes. Make sure that you keep a few reps in reserve as opposed to hitting muscular failure too soon. The idea is to do as many reps as possible in the allotted time and this is best done by resting as little as possible so aim to do
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as many sets of relatively low reps to achieve this. Staley suggests using a weight equal to your 10-12 rep max but initially only performing 6-8 repetitions per set. This allows multiple sets with minimal rest resulting in maximum workout density. As you near the end of the PR zone, start pushing the pace in an attempt to get as many reps as possible.
EDT is deceptively simple but the reality is it is a tough workout which requires focus and determination. It works very well for those seeking hypertrophy (muscle growth), muscular endurance or even strength if the correct loads are selected. One of the main benefits of EDT is that you know exactly how long a workout is going to last to the minute so it’s far easier to programme your exercise time. EDT training also works very well with body weight exercises. Here are a couple of EDT-style workouts:
Workout 1 1st 15-minute PR zone: dips and body rows 2nd 15 minute PR zone: squats and incline sit ups
Workout 2 1st 15-minute PR zone: handstand press-ups and chin-ups 2nd 15 minute PR zone: lunges and hanging leg raises
Aerobic Circuit Training ACT as the name suggests employs the use of a circuit purposely designed to increase CV fitness (and local muscular endurance). There are numerous ways to construct one of these types of circuit, but all need to include – along with a number of resistance exercises – a designated number of CV activities, such as running, cycling or skipping. You can include the CV aspect at the end of each circuit or between each exercise. Here are some examples:
ACT Workout with CV element at end of each circuit Perform standard circuit exercises such as press-ups, sit-ups, burpees, triceps dips, planks, squats, crunches etc on a time on/time off basis. At the end of each set run for, for example 5 minutes. You can use your heart rate monitor to control the level of intensity of the workout. If you are of an intermediate level of fitness, for example, then keeping your heart rate at 80% of max throughout the workout will have a substantial effect on maintaining and developing aerobic fitness. If you organise the exercises as per the PHA workouts previously described then the metabolic demands of the circuit will increase further (rather
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than performing same body part exercises one after the other). Perform the exercises rhythmically in order to maintain the heart rate levels required to make the workout aerobic.
To push the demands of the circuit into anaerobic territory then sprints can be performed at the end of each circuit. Try doing 4-6, 20m sprints with a walk back recovery (itself a form of interval training). You will probably be near to max heart rate by the time you recommence your circuit and unless you are of real, advanced fitness, will need to use recovery between the exercises to get your heart rate level down before the sprints are attempted again. Given the sprint aspect of this sample workout, performing exercises for 20sec and taking a 30sec recovery should be possible for someone of intermediate fitness. Another way to set this circuit up would be by selecting a designated number of reps to perform for each exercise. These should err on the side of achievability, to allow you to complete the circuit. The number of circuits and the exercises that you perform will of course reflect the level of your fitness.
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Some frequently asked questions about interval training
How long should each interval session last? There’s no ‘ideal’ length of an interval session. The length of a session will be dictated by the length of each intervals, the number of repeats and the rest period taken in between each interval. Two similar interval sessions targeting the same energy system could therefore be quite different in terms of total duration. For example, a session of 60-second intervals to target the lactate system could be as short as 10 minutes (5 x 1-minute intervals with one minute of rest in between), or as long as (12 x 1-minute intervals with 4 minutes rest in between) one hour. The number of repeats and the amount of rest time will be governed by your own fitness level and how hard you work at each interval.
What’s the best work interval length for me? This depends entirely on your goal. If your sport relies on intense burst of power then shorter, more intense intervals (30 seconds or less) will fit the bill best because they will more effectively target the anaerobic energy systems. Long distance endurance athletes on the other hand will benefit from much longer intervals (1-5 minutes). For general health fitness, short, high-intensity intervals appear to work well because they yield good gains in fitness for very little time invested.
How many interval repeats should I be doing? This will depend on your fitness and level of experience. At the very minimum, you should be able to complete 4 intervals, though 5 or even 6 are better still. There’s little evidence that going beyond 10 intervals (especially when the interval length is medium to long) is worthwhile because extra the training load imposed on the body isn’t matched by the potential gains. As a very rough guide, 8-10 repeats of intervals of 30 seconds or less works well. For longer interval lengths (30 seconds to 2 minutes), 6-8 repeats should suffice while for intervals longer than 2 minutes, 4-6 repeats should be ample. Of course all this will depend on how much rest you take and your current level of fitness. If you find you’re struggling to maintain your pace in each interval as the session progresses, you’ve either scheduled too many intervals or haven’t taken enough rest in between or are working too intensely (or a it’s because of a combination of these three factors)!
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Can I do consecutive days of interval training? You can but it’s not ideal. The odd back-to-back interval session probably won’t hurt you so long as you compensate afterwards by ensuring a longer than usual period of recovery/easy training. Also, bear in mind that if you’ve worked very hard on day 1, the quality of your interval session on day 2 is likely to be reduced somewhat.
What proportion of my total training volume should consist of intervals? Again, there’s no hard and fast rule. In some sports such as swimming, the majority of training sessions comprise of intervals. In other sports such as running (where the pounding forces on the joints are that much greater), the proportion of interval training will be relatively small. Your own level of fitness and experience will also determine how much of your training should comprise of intervals. For recreational sportsmen and women who are training 3-4 times a week, one (properly targeted) interval session per week is probably ample. For more serious athletes who might be training 6 or more times per week, two sessions per week could be more productive, providing of course there’s time for sufficient recovery.
Is there a preferred time of day to do intervals? Biological rhythms affect physical performance. The most powerful of these rhythms is the circadian or daily rhythm. Studies have shown that most people have a circadian rhythm that peaks during the late afternoon and early evening. At this time, your core temperatures will typically be higher, your muscles more elastic and your body generally primed for activity. It’s no coincidence that many world records have been set during the late afternoon/early evening! If you have a choice therefore, interval training would be ideally performed at this kind of time. However, don’t worry if this is not possible as you will benefit from interval training at other times too. Probably, the only no-no is to try and interval train very early in the morning when you’ve just rolled out of bed. Your core temperature at this time will be relatively low and muscles stiffer from inactivity. If you have to train very early in the morning, this is the time to do some gentler, steady-state training!
I’m recovering from injury – can I interval train? By its very definition, interval training is relatively intense. Like all intense exercise, the loading on joints, muscles and ligament is significantly higher than during gentle exercise performed at a steady-state intensity. Those recovering from injury therefore are not recommended to undertake interval training until a full recovery has been made.
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I’m prone to injury – will intervals increase my injury risk? Not necessarily. Provided you execute your interval sessions with good form and allow plenty of rest and recovery, a previous history of injury need not be a barrier to interval training. Caution however is the name of the game. You should ensure that you work your way gently into any interval training, particularly if you are intending to perform high-intensity intervals. You should also be prepared for the fact that you may need extra recovery compared to others. If in any doubt, it’s best to discuss your situation with a coach or physiotherapist, who will be able to give you more specific advice.
Are my nutritional requirements different when I interval train? Yes and no. In one sense, your nutritional requirements are not really that different from those required to support a general training programme – ie plenty of whole unprocessed carbohydrate (wholegrain bread and cereals, pasta, wholegrain rice, starchy vegetables such as potatoes, sweets potatoes, yam, beans, peas and lentils etc) to provide the high-grade fuel your muscles need for vigorous exercise, high- quality sources of protein (fish, lean cuts of meat, low-fat cheeses and yoghurts etc) to help muscle recovery and repair, a regular intake of nuts, seeds and fatty fish to provide the essential oils required for health and metabolism, plus of course plenty of fresh fruits and vegetables fluids for maximum health and antioxidant protection. All this of course assumes you’re also drinking plenty of fluid, including fresh water.
There is, however, a difference on emphasis; because interval training is by its very nature relatively intense, it’s even more important to ensure you keep your muscle stores of carbohydrate (glycogen) topped up. This is because even a slight drop in muscle glycogen levels can result in significantly more fatigue – something you definitely don’t want when commencing an interval session! Therefore, the day before an interval session, it’s imperative you consume plenty of carbohydrate, especially if that day includes a training session. It’s also a good idea to ensure that you consume a reasonable amount of carbohydrate in the hours before your interval session – and plenty of fluid too. Research shows that slower-releasing carbohydrates (eg oats and oat cereals, beans and lentils etc) are preferable in the hours before a hard exercise session as they help to keep blood sugar (and therefore energy levels) on a more even keel than fast-releasing, sugary carbohydrates.
The second difference in emphasis is on the period of recovery following intervals. As you might expect, it’s important to consume plenty of carbohydrate
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soon (within an hour) after training. Not only do you need to replace the muscle glycogen you have just used to fuel your intervals, your muscles are also primed to absorb carbohydrate most efficiently right after exercise. However, in addition to consuming carbohydrate, your muscles will also need some quick-releasing, easily digested protein. This is because the intense nature of intervals imposes a higher loading on muscles, which inevitably results in more tissue damage and breakdown. Consuming some protein along with your post-interval carbohydrate will help accelerate muscle recovery and repair. Indeed, studies have shown that, compared to carbohydrate only, the consumption of combined carbohydrate/ protein after intense training helps to accelerate recovery and readiness for a subsequent bout of training. An excellent way to ensure your muscles obtain the right combination of nutrients after an interval session is to consume one of the many commercially available recovery drinks. These should be of the low-fat variety and should provide a carbohydrate/protein ratio of around 3/1 with the protein preferably supplied as whey protein, which can be broken down and absorbed rapidly by recovering muscles.
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