LAB III Energy Cost of Exercise, Efficiency of Movement, & Body Composition It is important to remember that every change that takes place in the body during exercise is directly, or very closely indirectly, related to supporting the metabolic processes of the tissues (e.g. delivery of oxygen to the working muscle) or dealing with the consequences of those metabolic processes (e.g. dissipating excess metabolic heat). That is, understanding the metabolic processes in the working muscles is central to understanding exercise physiology. In the previous two labs we have studied oxygen consumption during steady state exercise and during graded exercise tests. In this lab, we return to using steady state oxygen consumption, but this time we will use it to help us determine the metabolic cost of the exercise. If one performs exercise that is principally aerobic in nature, then oxygen consumption reflects the energy expended via aerobic metabolism. Knowledge about the aerobic energy cost of activity is relevant to understanding 1) the role of exercise in weight management and 2) understanding the economy, or efficiency, of movement, which is an important predictor of endurance performance. To fully grasp these concepts, students will also learn procedures that are used to determine body composition and in calculating work accomplished on an ergometer.
Physics, Forms of Energy, & Units Related to Studying Energy The human body, like any other engine, operates within the laws of physics. It obeys the law of conservation of energy; the energy that appears as work must have previously entered the body in the form of food. Work is a form of energy. However, nothing, and no one, is 100% efficient. Thus, energy must be expended in excess of the amount of worked performed. According to the law of conservation of energy, the energy that does not result in work does not disappear, but rather, changes forms; in this case it is given off as heat During today’s lab, in addition to learning how to calculate energy expended, students will learn how to calculate power output during exercise and work accomplished using a variety of ergometers. An ergometer (ergo = work, meter = measure) is a device that allows the amount of mechanical work accomplished to be determined. The apparatus enables subjects to perform prescribed amount of work while physiological data can be measured simultaneously with stationary instruments. It is important that students do not confuse work accomplished with energy expended, even though they are closely related. The energy expended during exercise is at least three to five times the work accomplished during exercise. As you learned in human physiology, humans are usually only 20-30% mechanically efficient. This means that if a subject expends 100 kilocalories (energy expended), they will only be able to accomplish 20-30 kilocalories of work on an ergometer (work accomplished). According to the first law of thermodynamics, energy can not be created or destroyed; the remaining 70-80% of the energy expended by the subject’s body during the exercise bout is given off as heat. In this lab, students will learn to calculate power and work accomplished on treadmill and cycle ergometers. Guidelines for calculating power and work accomplished are also provided in the lab manual for determining the work accomplished using arm crank ergometers, bench step ergometers, and rowing ergometers. Before learning to calculate work accomplished it may be necessary for some of you to review the following definitions: Mass – Mass is the quantity of matter in a body. It is measured in units of grams, or more frequently in this class, kilograms. 1kg = 2.2 pounds. Force – Force is the cause that puts an object at rest into motion. According to Newton’s
Lab III - 1 second law of motion the rate of acceleration of an object is directly proportional to the force that acts upon it and indirectly proportional to the mass of the object. Therefore force can be calculated as follows: Force = Mass x Acceleration. The effect of the acceleration of gravity (9.8 m/s 2) on a mass produces a force measured in units called Newtons. Newtons = Mass (Kg) x Acceleration (9.8 m/s2) Work - A force that acts over a set distance results in work. It is measured in Newton- meters or Joules (1 Joule = 1Nm). A Joule can easily be converted into kilocalories by multiplying the number of Joules by 0.00024. Thus Joules and kilocalories are both units of work. Work is a form of energy. Later this quarter we will also use these units when calculating energy expended. Power – Power is the rate at which work is accomplished (or work accomplished per unit time). Power is measured in Watts. One Watt is equal to 1 Joule per second. In older exercise physiology literature the units of Kgm/min (kilogram meters per minute) were frequently used, although it was not technically a unit of power. Thus, this unit was given a a new name, a kilopond (Kp). One kilogram of mass is defined as exerting one kilopond of force. Therefore Kgm/min is equal to Kpm/min. We will not use these units in this class but you should be familiar with them as you will see them in older scientific literature and in some calculations of energy expenditure during exercise. Table 1. Common conversions used in this class. 1 Kp = 1 Kg 1 Kg = 2.2 pounds 1 inch = 2.54 cm or 0.0254m 1 mile = 1.6 Km or 1,600m 1 Kgm = 9.8 Joules 1 Ftlb = 0.1383 Kgm 1 HP = 745.7 Watts 1Kgm/min = 0.1633 Watts 1 Joule = 0.00024 Kilocalories 1 Watt = 1 Joule/sec = 0.00024 Kilocalories/sec Many factors influence the physiological response to exercise. Two attributes of an exercise bout that influence the physiological response to exercise, intensity and duration, are of particular importance for today’s lab. The intensity of an exercise bout is frequently presented in Watts, which are a unit of power. Thus, the rate at which work is accomplished is a major determinant of the intensity of the exercise bout. Because the intensity of an exercise bout is such an important determinant of the physiological response to exercise, repeated exercise tests or work bouts require the use of ergometers. For example if you want to compare some physiological variable (e.g. heart rate) before and after exercise training, you will need to use the same specific workload before and after training in order to make valid comparisons. Again, power is the rate at which work is accomplished. The ability to use or prescribe a precise exercise power output is essential for exercise-related research, serial fitness evaluations and exercise prescription. Thus, ergometers are an essential laboratory tool for all exercise professionals. In a research setting, ergometers are very important because it is necessary to control intensity. Likewise, in a clinical setting it would not be appropriate to tell a heart patient to simply say, “go exercise”; too much exercise may be risky for the patient and too little may not yield optimal results. Thus, the use of an ergometer allows the exercise professional to prescribe a specific workload to a patient. Lab III - 2 Understanding and Calculating Work and Power Whereas the power output during an exercise bout determines the intensity of the exercise bout, the work accomplished during an exercise bout is determined by both the power output and the duration of the exercise bout. Thus, if one wants to accomplish more work (and thus expend more energy) the intensity (power) of the exercise bout or the duration of the exercise can be increased. There are many ways to calculate work and power from each of these ergometers. These calculations will be much easier for you if you recognize the similarities in these calculations between the different ergometers. For example, the only major difference between how you calculate power or work between the different ergometers is in the calculation of velocity. One way that you can keep from getting overwhelmed by these formulas is to consistently perform them in the same order. For example, you could organize your calculations as follows: A) calculate kg from pounds (if necessary) B) calculate Force in Newtons (kg x 9/8m/s2) C) calculate velocity in meters/second D) calculate power in watts (Force x velocity, or Newtons x meters/second) E) calculate work in joules (Power x duration of the exercise bout, or Watts x seconds) F) calculate work in kcal (Joules x .00024kcal/J) Usually the intensity, or power, that the subject is to perform is known and the corresponding ergometer settings must be determined by using the following formulas backwards. Thus, students are expected to be able to perform these calculations forwards AND backwards! Students are expected to figure out, on their own (with help if necessary), how to perform these calculations backwards. It is also important to note that students may need to set subjects up on these ergometers at the appropriate intensities during practical exams.
Determining the Aerobic Energy Cost of an Exercise Bout The human body, like any other engine, operates within the laws of physics. It obeys the law of conservation of energy; the energy that appears as work must have previously entered the body in the form of food. When we work we must consume a certain quantity of oxygen to ensure the adequate release of energy derived indirectly from food to perform this work. If the work is not too strenuous, the energy demands may be met almost totally by the oxygen consumed during exercise and this is referred to as aerobic work and thus oxygen consumption can be used as an indicator of energy cost. However, if the exercise is very strenuous, the release of energy might have to be carried out with an oxygen deficit since the energy demands could be greater than the physiological systems capability to deliver oxygen. The body has a limited capacity for energy expenditure. The maximum rate of energy use for an untrained subject is about 2 horsepower (HP), which can be maintained for only a few seconds, and the all-day activity level is about 0.2 HP. Some competitive oarsmen have achieved energy expenditures in excess of 3.5 HP for a 6 minute exercise. Please keep in mind that energy expenditure is different from work accomplished. Energy expenditure is the amount of energy used by the body to perform an activity, whereas work accomplished is dependent upon how the distance over which a force was applied (e.g. a subject moving their body mass against gravity while on a treadmill).
Lab III - 3 Oxygen consumption is not only related to energy expenditure but to heat production as well. However, oxygen consumption is reported in L/min, which is not a unit of energy, so it must be converted to an energy equivalent. If a subject is using only carbohydrates as an energy source, then one liter of oxygen consumed is the equivalent of 5.05 Kcal of heat production. The use of these equivalents, frequently referred to as caloric equivalents, can be very useful for assessing energy expenditure during exercise or for determining a subject's metabolic rate. Because the caloric equivalents are different depending on the fuel substrate being used by the body, the type of substrate combusted must be known in order to determine the caloric equivalent. Caloric equivalents are usually obtained from well established tables. The RER chart in your Appendix (page 54) is an example of one of these tables. After determining the subject's VCO2 and VO2, the respiratory exchange ratio (RER) can be calculated (remember it is the proportion of CO2 expired to O2 consumed). Once the RER is known, the caloric equivalent can be obtained from the table. Energy expenditure, measured in Kcals, can then be calculated by multiplying the subject's VO2 (in L/min) times the caloric equivalent (in Kcal/L), and then multiplying times the number of minutes of exercise. One of the purposes of today's lab is to learn how to calculate energy expenditure during steady state (below anaerobic threshold) exercise and to use this to determine mechanical efficiency. You will also make a comparison of mechanical efficiency between two forms of exercise. To perform these procedures you must remember that the amount of oxygen consumed during exercise represents the oxygen required to perform the exercise as well as the amount normally needed to support life. The total amount of oxygen consumed per minute during exercise is called the gross oxygen consumption, and it represents not only the oxygen needed to perform the activity, but also the amount of oxygen needed to support life. Because we want to determine the energy cost of the activity we do not want to include the oxygen that would normally be needed just to support life. Thus, the amount of oxygen needed to perform the exercise, referred to as the net oxygen consumption, can be calculated as follows:
Net VO2 = Gross VO2 - Rest VO2 Using oxygen consumption and RER the energy cost of exercise can be expressed in kilocalories but the units of metabolic equivalents (METs) are also sometimes used. One MET is theoretically equal to the subject's resting metabolic rate, which is approximately a metabolic rate 2 of 35-41 Kcal/m /hr in college age students, or a VO2 of 3.5 ml/kg/min.
More on the Respiratory Quotient and Respiratory Exchange Ratio The ratio of the volume of carbon dioxide produced to the volume of oxygen consumed at the cellular level is known as the respiratory quotient (RQ). As discussed in previous labs, the respiratory exchange ratio is an estimate of the RQ. The RQ for carbohydrate metabolism is 1.00 whereas for fat it is about 0.70. This is because oxygen and hydrogen are present in carbohydrate in the same proportions as water, whereas in various fats extra oxygen is necessary for the formation of water. This can be demonstrated by the following reactions:
Carbohydrate: C6H12O6 + 6 O2 6 CO2 + 6 H2O RQ = 6 CO2 produced / 6 O2 consumed = 1.00
Fat: 2 C51 H98O6 + 145 O2 102 CO2 + 98 H2O
RQ = 102 CO2 produced/ 145 O2 consumed = 0.703
Lab III - 4 An average RQ for protein is about 0.82. However, determining a caloric equivalent for protein is much more complex because proteins contain nitrogen in addition to oxygen, hydrogen and carbon atoms. The nitrogen derived from protein metabolism is not given off by the lungs, but rather is excreted via the urinary system. Thus, determining the amount of calories coming from protein metabolism is very complex. The bulk of the calories expended by humans at rest, and during exercise, are derived from fats and carbohydrates. For this reason, and because of difficulties in assessing energy derived from protein metabolism, a non-protein RER is frequently used. Under resting conditions or during low intensity exercise the RER will usually be an accurate estimate of the RQ and will allow for an accurate assessment of metabolized nutrients and the caloric equivalent of oxygen consumed. For example, an RQ of 0.82 represents a blend of 40% carbohydrates and 60% fats at a caloric equivalent of 4.875 Kcal/L of oxygen consumed. By using this ratio and tables that include caloric equivalents for oxygen accurate metabolic rates can be determined. However, during intense exercise the relationship between carbon dioxide produced and oxygen consumed is complicated by the respiratory system’s function as a buffering mechanism. It is not uncommon to obtain RER values of over 1.00 during moderate to high intensity exercise, due to the buffering of the blood. When the body increases its reliance on anaerobic metabolism, lactic acid production increases. Under normal physiological conditions, one of the hydrogen ions associated with the lactic acid dissociates (thus we frequently refer to it by the name of its salt, lactate). The body can only tolerate small changes in pH, and thus must buffer the increase in hydrogen ions associated with the increase in production of lactate. The following formula is frequently referred to as the bicarbonate buffering system , and it is one quick mechanism by which the body can reduce the pH of the blood and other body fluids.
+ CO2 + H2O = H2CO3 = H + HCO3 carbon water carbonic hydrogen bicarbonate dioxide acid ion ion The bicarbonate buffering system helps to lower H+ concentration in the blood as follows. When there is an increase in hydrogen ions in the blood there will also be more carbon dioxide in the blood (according to the above equation these are all in equilibrium). These elevated levels of + H and CO2 stimulate an increase in ventilation (VE). When VE increases, it increases the rate at which CO2 is being expelled from the body by the lungs (an increase in carbon dioxide + production, VCO2), thus decreasing the amount of CO2 and H in the blood back towards normal.
Economy of Movement & Mechanical Efficiency If the amount of work done is measurable (i.e., Joules, "Kgm" etc.) and oxygen consumption is determined, it is possible to determine how much of the energy released results in the production of useful work. Mechanical efficiency is the percentage of energy released that results in work. Mechanical or work efficiency is calculated as follows: output (work accomplished) Mechanical Efficiency = x 100 input (energy expended) According to the first law of thermodynamics, the law of conservation of energy, the energy that does not result in the performance of work is converted to another form of energy; heat. The mechanical efficiency for most human physical activity is around 20 - 30% with 70 - 80% of the energy used ending up as heat. The non productive energy is due to energy loss Lab III - 5 during chemical to chemical and chemical to mechanical energy exchanges, as well as from energy used to overcome internal resistance or friction (in the muscles, joints, blood vessels, etc.), and results in the production of heat. Mechanical efficiency is affected by a number of things, including: biomechanical skill, training, muscle fiber type composition, muscle groups used, the type of exercise activity, various diseases, and the substrates being used by the subject to perform the activity. A smart student might write these down as a list so that it is easier to remember on exam days. VO2 at the anaerobic threshold (VO2-AT, discussed in future labs) is a major physiological determinant of endurance performance (the subject can work at higher work rates without accumulating lactic acid). If two athletes could run at this same VO2, then the more efficient runner could go faster for this rate of metabolism. It is therefore important that a distance runner have a running style or form that provides the greatest amount of work accomplished for the least amount of oxygen (or energy) utilized. This would translate to a faster running speed at VO2-AT. The determination of mechanical efficiency has been used to help runners develop their most efficient running style. In general, the more an athlete can minimize movements that do not directly contribute to the production of work, the greater their mechanical efficiency. Because many runners race on flat surfaces, and because treadmills require a percent grade/movement against gravity to calculate work accomplished, a related measure, running economy, can be calculated to reflect efficiency. Running Economy (ml/kg.km) = rel VO2 (ml/kg.min) x pace (min/km) Running economy at moderate to race paces are in the range of 160-220 ml/kg.km. A more economical runner (more efficient) would consume less oxygen for a given pace, and would thus be expending less energy. Typical numbers of untrained runners are in the neighborhood of 200 ml/kg.km and for elite runners are on the order of 180 ml/kg.km, suggesting elite runners expend less energy per unit distance moved. The energy cost of aerobic metabolism is usually determined indirectly by measuring the amount of oxygen consumed during the performance of a given activity. As will be discussed in future labs, the amount of energy provided by anaerobic metabolism is limited. However, if the exercise bout is below anaerobic threshold and steady state and is of constant intensity, then the energy cost of the first minute of exercise should not be different from the last minute of exercise. Therefore, the total energy cost (aerobic and anaerobic) of the first minutes of exercise (when the oxygen deficit is being produced) can be assumed to be the same as those that occur after steady state exercise is attained. Using these assumptions we can calculate the energy cost of the entire exercise bout based on the oxygen cost of the last minute. The determination of energy cost for constant work rate activities above "anaerobic threshold" can be estimated based on the linear relationship between work rate and oxygen consumption. Once this relationship has been established below "anaerobic threshold" the amount oxygen required for exercise intensities above "anaerobic threshold" can be predicted. This allows the estimation of total energy demand of the activity as well as the amount of energy supplied by aerobic and anaerobic pathways. This procedure is called the "Accumulated Oxygen Deficit" method. However, methods for estimating the energy cost of activities that are non- steady state and above anaerobic threshold require making several assumptions, and thus are not always completely accurate. Some of these will be used in future labs.
Body Composition & Fitness There are many methods to evaluate physical fitness. However, the definition of “fitness” for one person may not be adequate or appropriate for another person. Every individual has
Lab III - 6 unique demands placed upon them during the course of their normal daily activities, and thus require different “types” and/or “quantities” of “fitness”. One very broad definition of physical fitness is related to the ability of the person to meet the demands placed upon the body during their daily living tasks. Based on your daily living tasks, how would you define “physical fitness”? We have previously discussed the role of maximal oxygen consumption in describing physical fitness. Because a VO2max test requires at least a minimal amount muscular strength and endurance and stresses to a great extent the cardiovascular and pulmonary systems, this one number can say a lot about one’s fitness. While some consider VO2max as synonymous with “fitness”, it does not provide any information about other aspects of what have been called health related physical fitness attributes, which include the following: a) Cardiopulmonary endurance b) Flexibility c) Muscular strength d) Muscular endurance e) Body composition. VO2max obviously relates to cardiopulmonary endurance, and perhaps to some extent muscular abilities, but this still leaves us with an incomplete description of the subject’s health related physical fitness. In this lab we will also assess body composition. Obesity is a major risk factor for the development of coronary artery disease (CAD), the number one cause of death in the United States. 1 in every 2.4 deaths in the U.S. can be attributed to some type of cardiovascular disease. Not only is obesity a risk factor for developing CAD, it is also associated with poor blood lipid profiles (high cholesterol levels), diabetes mellitus, and hypertension. High cholesterol levels, diabetes mellitus, and hypertension are also major risk factors for the development of CAD. Not all major CAD risk factors are preventable or treatable, but obesity can be treated. It is true that genetics influences the tendency to become obese. However, increasing fat stores requires specific environmental conditions; specifically, chronic excess energy intake, chronic excessively low energy expenditure, or some combination. This means that it is, to some extent, treatable through diet, exercise, and in some cases medication. Obesity also has a negative impact on many fitness factors. The presence of obesity is best determined by assessing the subject’s body composition. However, all current methods for assessing body composition are imperfect. Not only are most methods for determining body composition inaccurate, they are frequently also time consuming and they can be expensive. The body mass index and waist-hip ratio are some fairly simple calculations that insurance companies have used in the past to estimate whether a population of subjects is obese or not. However, it is important to note that these are not measurements of body composition. The body mass index (BMI) is calculated as the subject’s mass in kg divided by their height (in meters) squared. A value of over 30kg/m2 is commonly used to suggest that the subject may be obese. It should be noted that in many cases a subject can exceed this value but not be obese (e.g. stocky, muscular individuals will be heavier for a given weight than people who are less muscular or stocky). Normal Values for Percent Body Fat of 20 to 29 Year Old Women and Men men women 90th percentile 7.1 % 14.5 % 70th percentile 11.8 % 19.0 % 50th percentile 15.9 % 22.1 % 30th percentile 19.5 % 25.4 % Lab III - 7 10th percentile 25.9 % 32.1 %
Body size and shape are largely determined by skeletal size, but are affected by the amount of muscle mass and other body tissues. The “ideal” body weight includes only a minimal amount of fat and depends largely on skeletal size. Early attempts to assess ideal body weight involved developing tables based on sex, height, age and weight. An individual simply weighed himself, and compared this weight to the “ideal” listed in the table. If his weight was greater than that listed he could be determined as “overweight”. However, these tables took no account of body composition. It was possible for an individual to have very little fat but be overweight, or to be underweight but have a relatively large percentage of body fat. We now have several methods to determine body composition, i.e., what proportion of the body weight is fat and what proportion is lean (lean body mass, or LBM). Using these methods one can determine if someone is actually “overfat” or obese, or if they are simply overweight because of greater than “average” muscle mass. Some of the methods used for assessing body composition are:
body densitometry (e.g. hydrostatic weighing) skin-fold thickness body diameters dual X-ray absorptiometry bioelectrical impedance
Weight loss and energy expenditure Being able to calculate energy expenditure during exercise can be very useful to if you are trying to help someone loose weight. It has been suggested that to lose weight and keep it off, weight loss should not exceed one pound of weight loss per week for most individuals, with a maximal rate of weight loss of no more than two pounds per week. If weight loss at rates higher than two pounds per week is necessary, this should only be done with medical supervision. How do you go about losing one pound per week of fat weight? One pound equals 454 grams, and complete oxidation of one gram of fat yields 9 kcal, thus we would expect that one pound of fat weight would equal 4,086kcal. However, since adipose tissue contains some amount of protein, minerals, and water in addition to fat, one pound of body fat actually represents about 3,500 kcal of stored energy. So, if you were to use exercise alone to accomplish this weight loss, with no change in diet, you would need to "burn" 500 kcal per day (3,500 7days/week). For a 150 pound female running a pace of ten minutes per mile, this translates to approximately 42 minute workouts every day. Not everyone feels comfortable running 10 minute miles and not everyone has 42 minutes a day to workout. Thus, for many people , a combination of dietary restriction and exercise may be the best bet. For example, the same female from above could do 21 minutes at the same intensity ("burning" ~250 kcal), and reduce caloric intake by 250 kcal/day, for a total of 500 kcal/day.
LABORATORY PROCEDURES A. Collect resting and exercise expired gas samples to determine oxygen consumption B. Calculate Power and Work Accomplished for your subject’s exercise Bout
Lab III - 8 C. Determine the aerobic energy cost of the exercise bout and then determine mechanical efficiency. D. Determine body composition of your subject and/or of a friend using hydrostatic weighing and/or skin fold measurements. E. Even if your subject is lean, perform a hypothetical weight loss calculation using the data you collected.
A. Collect resting and exercise gas samples 1. Collect a 5 minute sample of expired air during rest. While this sample is collected, some group members should obtain the ambient temperature, pressure, and water vapor pressure conditions which will be needed to calculate the STPD correction factor. After collecting the five minute resting sample, analyze the sample to determine those variables needed to calculate absolute VO2 (L/min): FEO2, FECO2, and the volume of the expired sample. Record your data. 2. Your subject will perform two 5 minute submaximal exercise bouts of known work rate on assigned ergometer. The exercise bouts should be low to moderate intensity and should definitely be performed below the anaerobic threshold. Expired air will be collected during the 5th and final minute of exercise. If the intensity is moderate or below, this should allow enough time to ensure that their VO2 has reached a steady state. Following analysis of collected air (as above) a second exercise bout will be performed on the assigned ergometer using the same work rate as the first work bout. Calculate the needed speed, grade, RPM, resistance, etc. to provide the same desired work rate as you did in the ergometry lab (lab 1). Remember,Watts = Joules/sec = Nm/sec = (kg X 9.8) m / sec.
B. Calculating Power Output and Work Accomplished Your instructor will assign your exercise bouts from among the following: Group Ergometer 1 Treadmill, forward and backward (same work rate) 2 Treadmill, walking and jogging (same work rate) 3 Bike, normal and low seat (same work rate) 4 Rower and Bike (same work rate) 5 Treadmill, 2 speeds (same work rate) 6 Bike, 2 different cadences/RPM (same work rate) 7 Bike, high and low work rate 1) Monark cycle ergometer This ergometer will be used on a regular basis in this laboratory and is considered a standard piece of equipment in many or most exercise physiology labs. Work is accomplished by the friction force of a belt around a fly wheel that results in the lifting of a resistance. The force that the pedals must overcome to make the flywheel move can be calculated by the effect of gravity on the resistance. The pedal revolution speed (RPM, revolutions per minute) and the distance traveled per full pedal revolution determine the distance upon which the resistance is acted. On a Monark cycle ergometer, each full pedal revolution would cause the ergometer to travel 6 meters if the device were not stationary. Thus, 6.0m/rev is a constant that you should commit to memory. Force = Kg x 9.8 m/sec2 = Newtons Lab III - 9 Velocity = RPM x 6 meters/revolution x 1min/60 sec = meters/sec Power = force x distance / time = Newtons x meters/sec = Nm/sec = J/sec = Watts Work = Power x time = Watts x (total work time, sec) = Joules Joules x 0.00024 Kcal/ Joule = Kcal The cycle ergometer is probably the most adaptable of the ergometers used in this laboratory because it allows for the easy measurement of several physiological variables (due to the fact that the person remains relatively more stationary compared to running, rowing or arm cranking). It also allows a wide range of work intensities. This ergometer requires a nearly identical energy expenditure for a given work intensity irrespective of sex, age or body size. However, it can be affected by mechanical efficiency. Mechanical efficiency on a cycle ergometer is influenced by several factors including training, pedal speed and seat height. Optimal pedaling frequency for most subjects is 50-75 revolutions per minute. This is because this is the range of RPMs in which most subjects have their greatest mechanical efficiency. On the other hand, trained cyclists may prefer pedaling closer to 90 or 100 revolutions per minute. For optimum mechanical efficiency the height of the seat should be adjusted to allow for an almost completely extended leg at the lowest pedal position. There should be an approximately 5 to 10 bend in the knee (170-175 between the upper and lower leg) when the pedal is at the bottom of its rotation. Alternatively, with the front part of the foot on the pedal and the leg extended with the knee only slightly bent, the seat height is proper if the heel is an inch (2.54 cm) below the front part of the foot. Although most people are familiar with this type of exercise it does not stress a large muscle mass (in comparison to treadmill exercise). Therefore a subject’s aerobic capacity determined on a cycle ergometer may be 5 - 10% less than on a treadmill or rowing ergometer. It is also more common for subjects to experience local muscle fatigue (quadriceps) during cycle ergometry exercise than during treadmill exercise because the workload is distributed amongst a limited muscle mass. Thus, a subject may be less likely to reach their “true” maximal exercise intensity on a cycle ergometer than on a treadmill. If the desired power is known and you need to work these formulas backwards in order to determine the correct combination of RPM and kg. It is important to remember what RPMs your subject(s) feel comfortable pedaling (see optimal pedaling frequency below). Choose an appropriate RPM and determine the velocity in meters/second at this RPM. Then work the formulas backwards to determine the necessary kg of resistance for the desired power.
2) Treadmill The motor - driven treadmill is one of the most commonly used exercise tools due to the universal skill of walking and running. The treadmill allows the calculation of work and power by knowing the speed and grade of the treadmill, the subject's weight and the duration of the exercise bout. The calculation of work requires that the force act against gravity. Thus, walking or running on a level treadmill does not result in the production of any work. The production of work by the subject requires that the grade of the treadmill be set at some level other than zero. The grade (or percent grade) of the treadmill is a ratio of the number of units of vertical distance traveled per 100 units of horizontal distance covered. For example, an 8.0% grade means that the subject would travel 8 meters vertically for every 100 meters traveled horizontally. Remember, when performing calculations percent values must be converted to decimals (e.g. use 0.08 if an 8% grade is used) Force = Body wt (Kg, pounds/2.2) x 9.8 m/sec2 = Newtons Lab III - 10 Velocity = Treadmill speed MPH x 1600 m/mi = meters/hour Meters/hour / 3600second/hour = meters/sec (forward) meters/sec (forward) x Decimal of % grade = meters/sec (up) Power = Newtons x meters/sec (up) = Nm/sec = J/sec = Watts Work = Watts x seconds ( total exercise time) = Joules Joules x 0.00024 Kcal/joules = Kcal If the desired power output is known, you will need to work these formulas backwards in order to determine the correct combination of speed (in mph) and grade. It is very important to know what are reasonable speeds and grades for most subjects. To perform the calculations backwards it is best to start by calculating the subject’s body mass in kg and their force in Newtons. Then determine an appropriate combination of speed and grade. In this class we will usually be using speeds between 3 and 10 mph and grades of 1-15%. However, one commonly used exercise protocol, the Bruce Protocol starts at a rather slow speed of 1.7mph and a rather steep 10% grade, and by the end of the test may be over a 20% grade (which is very steep). It is also a good idea to ask your subject if they walk or run on a regular basis, and if so, how fast. This will give you an idea what kind of speed they are capable of maintaining. Table 3. Speed in mph and walking/running pace Speed (mph) pace (min/mile) Speed (mph) pace (min/mile) 2 30 9 6:40 3 20 10 6 4 15 11 5:27 5 12 12 5 6 10 16 3:45 (pace of an elite miler) 7 8:35 22.5 2:40 (pace for a 10 second 100m) 8 7:30 70 0:51 (Cheetah running at full speed) The above table shows you the speed in miles per hour for a range of walking/running mile paces. Please note that most young, healthy people participating in an exercise regimen will not usually chose a speed slower than 3 mph during a workout (a moderate to brisk walking speed) and most normal healthy individuals would not go faster than a 6 min/mile pace (10 mph) for longer than a few minutes. Although most people are familiar with walking and running exercise the treadmill does pose some limitations in measuring physical and physiological variables. Energy is expended by the subject regardless of how steep the grade is. However, significant amounts of work are only accomplished when using at least a 5% grade (although it also depends on the speed). Thus we are somewhat limited in our ability to calculate the mechanical efficiency of exercise bouts performed using a low percent grade. Furthermore, neither work accomplished or mechanical efficiency can be calculated for an exercise bout on a flat treadmill (0% grade) because the subject has no vertical velocity (thus zero work would be accomplished). An additional concern is that a subject exercising on a treadmill must support his or her own body weight, as a result, work accomplished and energy expended are proportional to body size. This is unlike a cycle ergometer where a given rpm and resistance will be the same power output for all subjects regardless of their weight. Because of the large muscle mass used during running, most subjects will have a 5-10% greater aerobic capacity (VO2max, maximal ability to take up and utilize oxygen) on the Lab III - 11 treadmill than on the cycle ergometer. If the muscle mass used is large enough, aerobic capacity is usually centrally limited rather than peripherally limited (e.g. local muscle fatigue). 3) Bench Stepping Although bench stepping can be a rather boring form of exercise it does provide a simple means of measuring the rate of work accomplishment in a relatively stationary position. This test allows the measurement of work by knowing the subjects weight, the step distance and the step rate. The step rate can be maintained relatively constant by asking the subject to keep pace with the sounds made by a metronome.
Force = Body wt Kg (pounds/2.2) x 9.8 m/sec2 = Newtons Velocity = Step height (meters/step) x Step frequency (steps/min) = meters/min Recommended step heights : for male = 0.40 m, for female = 0.33 m meters/min / 60sec/min = meters/sec Power = Newtons x meters/sec = Nm/sec = J/sec = Watts Work = Watts x seconds ( total exercise time) = Joules Joules x 0.00024 Kcal/joules = Kcal Because there are now several accurate, commercially available ergometers this mode of exercise is no longer frequently used. However, it does provide a very repeatable means of exercise stress at a minimal expense and can be performed almost anywhere without the need for much equipment. It tends to underestimate mechanical efficiency due to the energy expended to lower the body (lowering the body does not accomplish any work). Intermediate step rates, between 20 and 30 ascents (steps) per minute, are the most comfortable, efficient, and yield the most consistent data. Low rates of ascent, 15 or fewer steps/minute, are more difficult than intermediate rates because the movement is discontinuous. High rates, 40 or more steps/minute can be dangerous and require concentration and exceptional power. When a high bench is used (.45 - .5 m) a stepping rate of 20-25 steps/per minute is optimal. One common fitness test, the Astrand-Rhyming fitness test, recommends a step rate of 22.5 steps/min. The rate of stepping has more influence on efficiency than the bench height. There are four movements per step (first leg up, second leg up, first leg down, second leg down). Thus, you will need to multiply the desired step rate times four to set the metronome frequency. For example, a metronome setting of 100 should result in a step rate of 25 steps per minute.
4) Monark arm crank ergometer The arm crank ergometer in this laboratory is a modified cycle ergometer for the use of the upper extremities. The calculation of work accomplished by the use of this device is identical to the procedure used with the leg pedaling ergometer. Because this device uses a relatively small muscle mass maximal power values (and maximal oxygen consumption values) on this device are much smaller than on the cycle ergometer. Furthermore, the exercise intensity at a given power outputs on an arm crank ergometer are much different from those listed in table 2. For example, 50-75 watts would most likely be a moderate intensity (or even a high intensity) on an arm crank ergometer; even though these power outputs would usually be a low intensity on a treadmill, cycle, or rowing ergometer. It is very important to keep in mind the fact that exercise utilizing different size muscle masses significantly alters the physiological response to exercise. The fact that arm cranking uses such a small muscle mass is of great utility for students and researchers trying to understand the role of muscle mass in determining the physiological Lab III - 12 response to exercise. It also can be an alternative mode of exercise for patients with orthopedic or mobility problems that preclude leg exercises. RPMs of 50 or 60 RPMs are usually recommended for arm crank exercise.
5) Concept II Rowing ergometer This device has been electronically calibrated to determine power output based on the speed of the flywheel and the affect of air friction on the rate of deceleration between strokes. An estimate of the power output can be obtained from the electronic display in Watts. Following the exercise an average power in Watts will be displayed. Use the average power to calculate work accomplished.
Work = Watts x seconds ( total exercise time) = Joules Joules x 0.00024 Kcal/joules = Kcal The rowing stroke is a smooth motion, requiring coordination between the muscles of the legs, torso, shoulders and arms. Although there are basically two parts to the stroke, the drive and the recovery, all of the movements are blended together smoothly and continuously. There should be no stopping at any point during the stroke. To Begin the drive, the rower reaches forward with knees bent, arms extended and body leaning toward the flywheel. The drive is begun with the legs and back doing all the work. The arms are straight and the shoulders are somewhat relaxed and performing a slight isometric action. Halfway through the drive, the legs and back are still doing all the work and the arms are still straight. Once the legs are fully, or nearly fully extended, the handle is pulled by the arms and shoulders into the abdomen. The legs are straight and the body is leaning back slightly. The first motion of the recovery is to bring the arms forward until they are fully extended and then the knees and hips are simultaneously flexed; brining the body forward. Allowing the arms to recover first puts the handle in front of the knees, thus avoiding interference between the knees and hands as the seat moves forward (additionally, if the person were actually rowing on water, lifting the hands over the knees would push the boat backwards. Once the body is drawn all the way forward with the legs bent and arms straight, the subject is now ready to begin the next stroke. Rowing obviously requires the use of a very large muscle mass. This allows skilled rowers to exercise at power outputs that would not be possible to maintain on ergometers using smaller muscle masses. Unfortunately not every person is familiar with the rowing motion, and as a result, inexperienced rowers tend to have low mechanical efficiencies.
C. Calculating Aerobic Energy Cost of Exercise
1. First calculate resting VO2 and VO2 for each exercise bout as you have done in previous labs. Then calculate the Net VO2 for each of the exercise bouts. Calculate the net energy cost of exercise once steady state has been reached (For the calculation of mechanical efficiency both input and output must be converted to common units for work or energy and this is best represented as kilocalories.):
VO2 = VEstpd (NF x 0.2093 - FEO2)
[Gross VO2 (L/min) - Rest VO2 (L/min)] = Net VO2 (L/min) 2. Calculate the RER during the exercise bouts, and determine the caloric equivalent from table in the Appendix. Calculate energy expended per minute as follows:
RER = VCO2 (L/min) / Gross VO2 (L/min) *look at table for Kcal/L Lab III - 13 Net VO2 (L/min) x caloric equivalent (Kcal/L) = Energy expended (Kcal/min) Energy expended (kcal/min) x # minutes of exercise = Energy expended (kcal) 3. After calculating aerobic energy expended, and using the work accomplished, calculate the (net) mechanical efficiency. ME% = (Work Accomplished / Energy Expended) x 100
D. Determine Body Composition of your subject and/or another student 1. Body Densitometry Underwater weighing is a technique based on Archimedes’ principle (do you know it?). The densities of bone and muscle tissues are higher than that of water, whereas fat is less dense than water. Thus a person with less fat will weigh proportionally more in water than a person of equal weight (in air) with more fat. To determine body density from underwater weighing, the following equation has been derived: Wa Db = (Wa-Ww) - (RV + 0.100 L) Dw Where: Db = body density, Wa = body weight out of water (in air), Ww = body weight in water, Dw = density of water (which varies with temperature of the water), RV = residual volume (in L), and 0.1L = the estimated air volume in the gastrointestinal tract The RV is the amount of air lift in the lungs after a maximal expiration. It can be estimated using the following equations: Males: RV = 0.019 H - 0.0115 A - 2.24 Females: RV = 0.032 H - 0.009 A - 3.9 Where H = height in centimeters, A = Age in years. If forced vital capacity (FVC) is known (from previous courses), RV can be more accurately predicted using one of the following formulas: Males RV = FVC x 0.24 Females RV = FVC x 0.28
Percentage of body fat is then determined using one of the following equations:
% body fat = 4.570 - 4.142 X 100 (Brozek Formula) Db or
Lab III - 14 % body fat = 4.950 - 4.500 X 100 (Siri Formula) Db
2. Anthropometric Measurements Anthropometry is the science that deals with the measurement of size, weight, and proportions of the human body. Measurements of skin-folds, circumferences or body diameters may be used to predict body density and percentage of body fat. In some cases these estimates may be inaccurate (e.g., in school children) and the measurements alone should be compared. Body density can vary with age, gender, race, and activity. Some population-specific equations have been developed. These may be important when estimates in strictly defined populations are required (e.g., elite athletes) but generalized equations also exist which can be used for the general population. These equations take age into account for potential changes in the ratio of internal to external fat and bone density. Separate equations exist for males and females.
Skin-fold measurement Skin-fold measurements are taken using specially designed calipers and are taken at specific sites. The following are the most common sites: a. Pectoral - diagonal fold taken halfway between the anterior axillary line and nipple (men); or one third this distance (women). b. Axilla - vertical fold on the midaxillary line at the level of the xiphoid process of the sternum. c. Triceps - vertical fold on posterior midline of upper arm (over triceps) halfway between acromion and olecranon; elbow should be extended and relaxed d. Subscapular - vertical fold on the vertebral border of the scapula, 1-2 cm below the inferior angle e. Abdominal - vertical fold 2 cm lateral to umbilicus f. Suprailium - diagonal fold above anterior iliac crest g. Thigh - vertical fold on anterior aspect of thigh, midway between hip and knee All measurements should be taken on the same side of the body. Muscles should be relaxed. Skin-fold should be firmly grasped between thumb and index finger, and calipers placed perpendicular to the fold one centimeter from the fingers. Three measurements should be taken at each site. Comparisons are best if same tester, same
Lab III - 15 calipers and same equations are used. Up to a ±3% variation in fat determination can be noted even with experienced testers using the same equipment on the same day!
3. Body Mass Index (BMI) This measurement compares an individual’s weight to their height as follows: BMI = Weight (Kg) / Height2 (m2). Normal values for BMI fall in the range of 18.5 to 24.9 kg/m2. Health problems associated with obesity increase if a subject has a BMI over 25 kg/m2. The American Heart Association uses a value of 30 kg/m2 to group patients as obese or not obese when assessing major CAD risks. It has been suggested that subject's who have a BMI between 25 and 29.9 kg/m2 are overweight and subject's with a BMI over 30 kg/m2 are obese. However, keep in mind that a body mass index is not a true measure of body composition (it does not really give us any indication of percent fat or lean tissue). For example, it is not uncommon for very lean, muscular subjects to have a BMI over 25, or even over 30, even though they are clearly not obese individuals. Remember to convert inches to meters (there are 0.0254 m/inch)
4. Waist to Hip Ratio (WHR) This measurement evaluates an individual's pattern of fat distribution, which has been found to be related to cardiovascular risk. The so called “apple” or male pattern of fat distribution is associated with a higher risk of type 2 diabetes, hypertension, and CAD, but the “pear” or female pattern is associated with a lower risk. Health risk is considered very high in young men if the WHR is over 0.94 and in young women if the WHR is over 0.82. This ratio is calculated from the measurement of the waist and hip girth measurements. The measurements are made as follows: Waist - measured at the narrowest point between the xiphoid process and the illiac crest (usually within an inch or two of the umbilicus). Hip - measured at the largest point at the level of the greater trochanter over the maximum protrusion of the buttocks. WHR = Waist (cm) / Hip (cm)
E. Perform hypothetical weight loss calculations 1. Calculate a new desired (ideal) body weight for your subject. fat mass = decimal of % body fat x body mass LBM = body mass - fat mass *Desired (ideal) Body weight = Current LBM / (1.0 - decimal of desired %BF) *This calculation is limited because it assumes that LBM does not change
2. Calculating how many minutes per day to lose this weight Remember that 1pound fat = 3,500 kcal 500 kcal/day to lose 1 pound/week
Lab III - 16 500kcal/day ÷ Energy expended in kcal/min = minutes/day
Lab III - 17 Data Sheets
A. Resting & Exercise Expired Gas Sample Data Subject Wt. Kg Ambient Temp. °C Ambient Pressure mmHg Water Vapor Pressure mmHg STPD Correction Factor ______
Rest Exercise 1 Exercise 2
a. FEO2
b. FECO2
c. Sample Volume (L)
d. Meter Volume (L)
B. Calculate Exercise Power & Work Accomplished Exercise Bout 1. Ergometer: ______Settings: ______Power (Watts):
Work Accomplished (kcal):
Exercise Bout 2. Ergometer: ______Settings: ______Power (Watts):
Work Accomplished (kcal):
Lab III - 18 C. Calculation of Energy Cost of Activity and Mechanical Efficiency
Rest Exercise 1 Exercise 2 ATPS Volume (L) a. (sample + meter vol.) VE min. Vol. ATPS ( by b. 5 if needed to get L/min)
c. VE STPD (L/min)
d. NF
Gross VO2 (L/min) e. (rest or exercise VO2)
f. VCO2 (L/min)
g. RER Caloric equivalent h. (Kcal/L)
i. Net VO2 (L/min)
= Gross VO2 - rest VO2 Energy Expended j. (kcal/min) = Net VO2 x Caloric Equiv.
k. Energy Expended (kcal) Work Accomplished (kcal, l. from above) Mechanical Efficiency m. (%)
How did mechanical efficiencies compare between exercise bout 1 and exercise bout 2? If they were different explain why?
Did you get reasonable answers for mechanical efficiency? If not try and explain why?
If your subject was on a treadmill, calculate running economy in ml/kg.km. If not, what would be the running economy of a 170 pound male running 9 mph with a VO2 of 4.5 L/min?
Lab III - 19 How are the concepts of running economy and mechanical efficiency related?
For exercise bout 1, what percent of calories came from carbohydrate metabolism? How about fat metabolism?
How many total calories were expended in exercise bout 1, and how many of these calories were from fats? How many calories from carbohydrate?
Class data for mechanical efficiency – will be covered at end of class Exercise Bout 1 ME% Exercise Bout 2 ME%
group 1
group 2
group 3
group 4
group 5
D. Body Composition & related data 1. Hydrostatic Weighing Data (Demonstration, use formulas from above) Subject 1 (m/f) Subject 2 (m/f) Height: ______Weight in air: ______Dw ______FVC (if known): ______Estimated RV: ______Weights in water (at least 3) ______Average weight in water: ______Body Density: ______Lab III - 20 % Body fat: ______
2. Skin-fold Data Assess body composition using skin-fold measurements from at least one member of your group. You can use the nomogram on appendix page 68 instead of using the long body density formulas below. Females a. Body Mass ______kg b. Skin-fold thicknesses (in mm) – take three measurements at each site Triceps ______average= ______mm Suprailiac ______average= ______mm Anterior thigh ______average= ______mm c. Determine the mean skin-fold thicknesses and use these values in the next equation. d. Body Density = 1.0994921 - 0.0009929 (Sum of the three sites) + 0.0000023 (Sum of the three sites)2 -0.0001392 (Age) Body Density = ______e. Plug the body density value into either the Siri or Brozek formula (one of the two equations given for hydrostatic weighing) to determine % BF. Then calculate your subject's fat mass and lean body mass. % Body Fat ______Fat mass ______LBM ______Males a. Body Mass ______kg b. Skin-fold thicknesses (in mm) – take three measurements at each site Pectoral ______average= ______mm Umbilicus ______average= ______mm Anterior thigh ______average= ______mm c. Determine the mean skin-fold thicknesses and use these values in the next equation. d. Body Density = 1.10938 - 0.0008267 (Sum of the three sites) + 0.0000016 (Sum of the three sites)2 - 0.0002574 (Age)
Body Density = ______
e. Plug the body density value into either the Siri or Brozek formula (one of the two equations given for hydrostatic weighing) to determine % BF. Then calculate your subject's fat mass and lean body mass. % Body Fat ______Fat mass ______
Lab III - 21 LBM ______
How do the percent body fat obtained by skin-fold measurements compare to values obtained with hydrostatic weighing?
3 & 4. BMI and Waist to Hip Ratio Subject weight kg height cm waist girth cm hip girth cm BMI Is this normal? WHR Is this normal?
E. Weight Loss calculations: 1. Calculate a new desired (ideal) body weight for one of your subjects. For example, what would their new (ideal) body weight be if they wanted to reduce their percent body fat by 5%?
a. subject weight ______, % body fat ______b. fat mass ______c. LBM ______d. desired body wt. ______What is a potential limitation of the formulas we used for calculating desired body weight?
How many pounds would the subject need to lose to achieve this new ideal body weight?
How long would this take if they wanted to lose this weight at a rate of 1 pound per week? How about 0.5 pounds per week?
2. Using the energy expended, in kcal/min, from exercise bout 1, determine how many minutes per day your subject would have to exercise to lose a) one pound of weight per week and b) half a pound of fat per week. Assume they exercise seven days per week for this example. Show calculations below.
Lab III - 22 If your subject did not have this much time every day to exercise, what is another strategy for achieving this weight loss?
Study questions 1) One pound of fat is equivalent to 3,500 kcal. Calculate your fat mass in pounds and determine how many kcal of fat you have stored in the body. If you assume that you will expend around 2000 kcal/day with only basic activity, how many days could you survive on your fat stores? Impressive, isn’t it?
2) What are the limitations of calculating mechanical efficiency based on treadmill exercise?
3) What are some applied uses of mechanical efficiency?
4) Why is it possible to estimate the energy cost of a steady state, sub anaerobic threshold exercise bout based on the last minute of exercise ?
5) What factors affect mechanical efficiency?
6) Why does it make sense that mechanical efficiency is related to endurance performance?
7) Can you name three clinical, or disease, conditions that would be expected to reduce mechanical efficiency? Explain your answer.
Lab III - 23 8) Name the health-related physical fitness attributes. In your own words, how are each of these related to health?
9) Now that you have determined your percent body fat, what is your VO2max relative to your lean body mass?
10) On a separate piece of paper, explain the pros and cons of using the following methods for assessing obesity? Body mass index, waist to hip ratio, skin-fold measurements, hydrostatic weighing, bioelectrical impedance.
11) Why is body composition important when assessing health related physical fitness?
12) What power output ranges (in Watts) would you consider light, moderate, and heavy intensities if the subject were of average size and performing treadmill or cycle exercise? How many Kcals of work would be accomplished in 10 minutes at each of these power outputs?
13) What is a reasonable RPM and resistance for an average person to maintain on a cycle ergometer for 30 minutes if they desire a moderate workload? How about for a well trained cyclist?
14) If your subject was 25% mechanically efficient and they accomplished 50 kcals of work, how much energy did they expend?
Lab III - 24 15) Maximal power outputs, while using a moderate-to-large muscle mass, such as on a cycle ergometer, could be expected to be in the range of ______to ______Watts for college age females and ______to ______watts for college age males. During a Wingate test some subjects in this class may exceed ______Watts, but only for a few seconds. However, cyclists on the Tour de France may sustain power outputs of ______Watts for several hours at a time. Elite rowers who are tall, muscular, and very fit may sustain over ______Watts for six minutes.
16) How many weeks would it take a 300 pound man to lose 50 pounds at a rate of one pound per week? If his resting VO2 is .45L/min, and if he can exercise comfortably at a VO2 of 2.25L/min and a VCO2 of 2.0L/min, how many minutes per day would he have to exercise to lose one pound of weight per week (assuming he exercises 7 days/week)?
17) Sample calculations for work and power: I. What is the power and total work for a 70Kg individual pedaling the cycle ergometer at 75RPM and 2Kg resistance for 20 minutes.
II. What is the power and total work for a 65Kg individual walking on the treadmill at 3.5MPH and 5% grade for 30 minutes.
III. If an elite cyclist wanted to cycle at 350 Watts, what combination of RPM and kg resistance would you recommend for them?
IV. If a 160 pound subject were running 10 min/mile pace (remember to convert to miles per hour, see table 3) and wanted to exercise at 140 Watts, what percent grade should they use?
Lab III - 25