A significant challenge for the fitness professional occurs within the area of weight management of both personal training clients and athletes because even athletes sometimes allow their body composition to deteriorate from an optimal range. For nonathletes or recreational athletes, the improvement of body composition can be made the sole program goal, possibly with specific objectives regarding body fat and/or lean mass. For some clients, the fitness specialist may have the full toolbox of exercise variables available for programming, guided primarily by the client's preferences and, of course, by any medical restrictions. For athletes, though, especially when leading into important sport-specific training phases, such a situation may present potentially conflicting training program needs. Should there be exercise incorporated specifically for body fat loss? Could such exercising be detrimental to the athlete's recovery and adaptation to the training stimuli targeted by the fitness professional or could it be designed to avoid any negative impact or even contribute positively in the athlete's sport-specific training for future competitions?
One particular question stemming from all this pertains to the effect of maximal effort (all-out sprint) interval training in the context of fat loss. The issue brings into consideration the longtime debate regarding the effect of exercise intensity on fat loss. A recent study (1) examined the ability of an all-out sprint interval exercise session to contribute to energy expenditure. Male students from a kinesiology department performed the sprint protocol on one occasion, consisting of four 30-second bouts on a stationary cycle with a resistance of 100 g/kg of body mass. Each interval was followed by 4 minutes of light cycling. On another day, they performed a session of continuous endurance exercise at approximately 70% V[Combining Dot Above]O2max, lasting 30 minutes. Both protocols were initiated with a 7-minute warm up.
Regarding the debate on exercise intensity and fat loss, the intensity of sprint interval exercise itself does not fit within a "fat burning" (lower) intensity zone, which had gained some popularity for fat loss. The study examined respiratory exchange ratio (RER), providing a reflection of the proportion of energy derived from carbohydrate versus fat stores. With no differences between protocols in RER measurements after the acute RER rise of the session, the authors concluded that a shift in substrate use was unlikely. Therefore, for the sprint protocol to be as beneficial as the continuous protocol, it must match its overall energy expenditure and hypothetically include a similar amount of fat usage.
As might be expected, when compared with the continuous protocol, the sprint protocol caused a much lower exercise V[Combining Dot Above]O2, both in terms of the average consumption per minute, indicative of metabolic rate, and of the total oxygen consumption for the duration of the exercise session. Therefore, during exercise, the sprint protocol was not as costly calorically as the continuous protocol. When an 8-hour period was compared, from pre-exercise baseline to 6 hours postexercise, the sprint protocol had raised its total oxygen consumption by 37% over that of a control condition but the 8-hour oxygen use of the continuous protocol was still 17% higher than that of the sprint protocol. However, when the V[Combining Dot Above]O2 data were compared for the full 24-hour span, the sprint protocol resulted in oxygen use equal to that of the continuous exercise condition. Therefore, these protocols contributed similarly to the energy expenditure across a day that was otherwise controlled calorically in terms of physical activity and food intake. Consequently, the effectiveness of the sprint protocol must come from an elevated metabolism during the hours after the exercise session, in a sense making up for the lower oxygen use during exercise, to reach a similar 24-hour energy cost. Although the differences were not statistically significant at any single postexercise time point (right after exercise; at 2, 3, and 6 hours postexercise; and the following morning), the combined total excess V[Combining Dot Above]O2 of the continuous protocol over this time period was only 19% of that of the sprint protocol.
Previous studies have shown high-intensity interval sessions, equivalent to only 105–108% V[Combining Dot Above]O2max, to be effective in increasing excess postexercise oxygen consumption (EPOC). However, the thinking has been that such elevations and the accompanying rise in energy use may not have been substantial compared with the much larger energy cost associated with the exercise session itself (3). The most recent study, though, provides evidence that if the repeated effort is an all-out sprint, it can offer an EPOC that is significant to the practitioner. Whereas, during the session, the continuous protocol cost approximately 440 kcal, the sprint session cost only 175 kcal. During the remainder of the day, though, the sprint protocol cost approximately 250 kcal extra outside the session, bringing the 2 types of session to a 24-hour energy cost tie and adding further credence to the viability of sprint interval training for fat loss. This is not surprising in light of previous findings from the same laboratory; a 6-week training program using a running sprint interval protocol was at least as effective as a continuous endurance protocol in fat loss (2).
For the personal fitness trainer whose client's only issue is an overly pressed agenda on certain days, the sprint protocol may save time. The endurance protocol in the current study lasted 37 minutes, whereas the sprint protocol can be done in 21–25 minutes, depending on how long one chooses to pedal for the final active recovery interval. Therefore, if overall 24-hour caloric expenditure is important but training time is lacking for the client, this type of training protocol can be just as effective as one of longer duration and lower intensity, issues of intensity intolerance notwithstanding. For the strength and conditioning professional and the sport coach, these results add physiological support to the notion that overall fat loss does not necessitate a lower exercise intensity. It means that in addition to continuous endurance training, sprint interval training is a viable option when it makes better sense in the overall program of a particular athlete who needs to decrease body fat.
Strength and conditioning specialists can look to future research reports to confirm this effect in trained athletes. Hopefully, there will also be additional research to show if it is necessary to use maximal intensity or if a near-maximal intensity might suffice and if it is necessary to use 4 intervals with 4-minute rest periods or if a shorter session (fewer intervals and/or shorter recovery breaks) might suffice. In the mean time, although this study's results are specific to physically active young men, they lend further support to strength and conditioning specialists who are leaning toward this approach for their "power endurance" athletes who may need to lose body fat during a low-volume training phase.
1. Hazell TJ, Olver TD, Hamilton CD, Lemon PWR. Two minutes of sprint-interval exercise elicits 24-hr oxygen consumption similar to that of 30 min of continuous endurance exercise. Int J Sport Nutr Exerc Metab 22: 276–283, 2012.
2. Macpherson RE, Hazell TJ, Olver TD, Paterson DH, Lemon PW. Run sprint interval training improves aerobic performance but not maximal cardiac output. Med Sci Sports Exerc 43: 115–122, 2011.
3. McNeely E. The role of EPOC in weight loss programs. National Strength and Conditioning Association Hot Topic Series. May 2001. Available at: http://www.nsca.com/Education/E-learning/The-Role-of-EPOC-in-Weight-Loss-Programs
. Accessed: November 29, 2012.