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High-Intensity Interval Training: Applications for General Fitness Training Brad Schoenfeld, CSCS1 and Jay Dawes, MS, CSCS*D, NSCA-CPT*D2 1Global Fitness Services, Scarsdale, New York; and 2National Strength and Conditioning Association, Colorado Springs, Colorado

above the lactate threshold, close to HIIT also has been shown to be _ VO2max, and then carried out to a point superior when compared with steady- just before the onset of volitional state training for those attempting to . This high-intensity bout is then lose weight. While moderate-intensity followed by a low-intensity recovery steady-state aerobic (the so- period that allows the body to buffer called ‘‘fat-burning zone’’) results in an and clear lactic acid from the blood, increased percentage of fat burned thereby allowing the individual enough during a workout, total caloric expen- time to recover and perform another diture and lipolysis (i.e., fat breakdown) high-intensity interval. are substantially greater in an HIIT Paul Sorace, MS, ACSM RCEP, BENEFITS OF HIGH-INTENSITY protocol. The resulting effects on fat CSCS*D AEROBIC INTERVAL TRAINING loss are significant. This was apparent Column Editor Many traditional exercise training pro- in a study by Tremblay et al. (11), grams focus on the use of steady-state who compared 2 groups of subjects: an aerobic activity for the purpose of -trained group versus an SUMMARY substrate utilization. This makes sense HIIT-trained group. Despite a signifi- because the longer the duration of an HIGH-INTENSITY AEROBIC cantly lower energy cost of the HIIT INTERVAL TRAINING (HIIT) IS A activity, the greater the amount of workout at the end of the study (120.4 POPULAR STRATEGY FOR relative percentage of calories used that versus 57.9 MJ), participants in the IMPROVING CARDIORESPIRATORY come from fat storage. However, HIIT confers several advantages over steady- HIIT group experienced a 9-fold FITNESS AND , AS WELL AS state aerobic training. Research indi- greater reduction in skinfold thickness. REDUCING BODY FAT LEVELS. cates that cardiovascular adaptations Several factors appear to contribute to THIS ARTICLE WILL EXPLORE THE to exercise are intensity dependent, and this lipolytic advantage. For one, HIIT BENEFITS OF HIIT AND DISCUSS improvements in cardiovascular func- increases the body’s potential to use ITS APPLICATION FOR FITNESS tion via HIIT may be superior when lipids as an energy substrate to a greater TRAINING. compared with more traditional train- extent than steady-state aerobic exer- ing protocols (6,12). HIIT has shown cise, with an increased upregulation of _ greater improvements in VO2max, en- enzymes responsible for beta-oxidation igh-intensity aerobic interval dothelial function, blood pressure, (11). There also is an increased growth training (HIIT) is a popular cardiac contractility, insulin signaling, hormone response attributed to HIIT, H strategy for improving cardio- and contraction coupling when com- likely mediated through the significant respiratory fitness and health, as well as pared with moderate-intensity aerobic reducing body fat levels. A standard exercise (5,6,10). This has important lactate accumulation associated with HIIT protocol involves alternating implications not only for possibly this type of training (4). In addition, bouts of both high- and low-intensity preventing the onset of cardiovascular HIIT heightens the extent of excess exercise to increase the amount of disease but also in potentially reversing postexercise oxygen consumption (also high-intensity work performed during the risk of certain comorbidities for known as the ‘‘afterburn’’), which has an acute bout of training. High-inten- those suffering from cardiac and met- been shown to be positively correlated sity intervals are typically performed abolic disorders. with exercise intensity (1).

44 VOLUME 31 | NUMBER 6 | DECEMBER 2009 Copyright Ó National Strength and Conditioning Association Table ratio of 1:1 (7). These recommenda- context of his/her current fitness pro- Thirty-minute sample HIIT tions, however, are based on athletic gram as a whole. routine populations. For the general popula- tion, a variety of W:R ratios can be Interval, min RPE (scale of 1–10) employed in an HIIT routine. A 1:2 Brad Schoenfeld is president of 3 (warm-up) 3 W:R ratio, for instance, has been Global Fitness Services in Scarsdale, shown to produce favorable responses 45 New York. that enhance both aerobic and anaer- 17obic energy system development (8). Jay Dawes is the Education Director For those who are less fit, a 1:4 W:R 35 for the National Strength and Condition- ratio would probably be more appro- ing Association in Colorado Springs, 18priate, allowing acclimation into a more Colorado. 15intense HIIT routine. W:R ratios can be varied throughout the course of 19a workout based on individual fitness 15levels (see sample routine in the Table). REFERENCES Because of the intense nature of the 19 1. Bahr R and Sejersted OM. Effect of routine, those engaging in HIIT need intensity of exercise on excess postexercise 15 to be cognizant of the potential for O2 consumption. Metabolism 40: 836– 19overtraining. A study by Billat et al. (2) 841, 1991. noted that, despite an increase in 2. Billat VL, Flechet B, and Petit B. Interval 15 _ plasma noradrenaline, performance training at VO2max: Effects on aerobic 19variables were not altered by 4 weeks performance and overtraining markers. _ Med Sci Sports Exerc 31: 156–163, 1999. of intensive training at VO2max. Lon- 25ger periods of sustained interval train- 3. Gibala MJ and McGee SL. Metabolic 18ing have not been studied, however, adaptations to short-term high-intensity and might increase the risk of an interval training: A little pain for a lot of 35 gain? Exerc Sport Sci Rev 36: 58–63, overtrained state. 2008. 17 While HIIT has been shown to 4. Gray AB, Telford RD, and Weidemann MJ. 3 (cooldown) 3 significantly improve cardiovascular Endocrine response to intense interval function and stimulate greater weight exercise. Eur J Appl Physiol Occup Physiol HIIT = high-intensity aerobic interval 66: 366–371, 1993. training; RPE = rating of perceived exertion. loss compared with traditional steady- state aerobic training protocols, cau- 5. Haram PM, Kemi OJ, Lee SJ, Bendheim MØ, tion should be exercised when using it Al-Share QY, Waldum HL, Gilligan LJ, Finally, HIIT is a very time-efficient as a prescription for the general fitness Koch LG, Britton SL, Najjar SM, and Wisløff U. Aerobic interval training vs. form of training. As few as 6 sessions of population, particularly in those with HIITover a 2-week period for a total of continuous moderate exercise in the cardiovascular disorders. It is impor- metabolic syndrome of rats artificially about 15 minutes of very intense tant that a solid base of cardiorespira- selected for low aerobic capacity. exercise (equating to approximately tory fitness be established prior to Cardiovasc Res 81: 723–732, 2008. 600 kJ or 143 cal) have been shown integrating HIIT into a client’s strength 6. Kemi OJ, Haram PM, Loennechen JP, to increase oxidative and conditioning program. Osnes JB, Skomedal T, Wisløff U, and capacity and alter metabolic control Ellingsen Ø. Moderate vs. high exercise during aerobic-based exercise (3). And In sum, HIIT can be a time-efficient intensity: Differential effects on aerobic 7 HIIT sessions performed over 2 means to improve cardiorespiratory fitness, cardiomyocyte contractility, and weeks significantly heightened whole fitness and reduce body fat levels over endothelial function. Cardiovasc Res body and skeletal muscle capacity for and above what is possible through 67: 161–172, 2005. fatty acid oxidation during exercise in steady-state aerobic training. However, 7. Reuter BH and Hagerman PS. Essentials moderately active women (9). For those given the high-intensity nature of the of and Conditioning who have limited time to work out, this protocol, HIIT may be associated with (3rd ed). Baechle T and Earle R, eds. an increased potential for overtraining, Champaign, IL: Human Kinetics, 2008. makes HIIT an intriguing option. pp. 499. especially when combined with regi- PERFORMANCE ISSUES mented resistance training. It is there- 8. Rozenek R, Funato K, Kubo J, Hoshikawa M, and Matsuo A. Physiological responses to The general prescription for interval fore essential to consider the previous interval training sessions at velocities _ training is to employ 3- to 5-minute training experience and abilities of the associated with VO2max. J Strength Cond work bouts with a work to rest (W:R) trainee and integrate HIIT within the Res 21(1): 188–192, 2007.

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9. Talanian JL, Galloway SD, Heigenhauser GJ, Bonen A, and Spriet LL. Two weeks of high-intensity aerobic interval training increases the capacity for fat oxidation during exercise in women. J Appl Physiol 102: 1439–1447, 2007. 10. Tjønna AE, Lee SJ, Rognmo Ø, Stølen TO, Bye A, Haram PM, Loennechen JP, Al-Share QY, Skogvoll E, Slørdahl SA, Kemi OJ, Najjar SM, and Wisløff U. Aerobic interval training versus continuous moderate exercise as a treatment for the metabolic syndrome: A pilot study. Circulation 118: 346–354, 2008. 11. Tremblay A, Simoneau JA, and Bouchard O. Impact of exercise intensity on body fatness and skeletal muscle metabolism. Metabolism 43: 814–818, 1994. 12. Wisløff U, Støylen A, Loennechen JP, Bruvold M, Rognmo Ø, Haram PM, Tjønna AE, Helgerud J, Slørdahl SA, Lee SJ, Videm V, Bye A, Smith GL, Najjar SM, Ellingsen Ø, and Skjaerpe T. Superior cardiovascular effect of aerobic interval training versus moderate continuous training in heart failure patients: A randomized study. Circulation 115: 3086– 3094, 2007.

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