Do sprint intervals to lose fat and improve conditioning—save time too. Research shows that high-intensity sprints are the only form of conditioning to produce significant fat loss. Plus, a new study found that high-intensity training will increase both anaerobic and aerobic capacity more than steady-state endurance exercise.
This new study, published in the Journal of Sports Science and Medicine compared the effect of a 4-month sprint interval running program with an endurance running program on body composition, aerobic capacity, and time in a half-marathon race. The sprint interval protocol varied each day, but an example of one of the workouts used was 10 intervals of 30-sec all-out sprints with 90 seconds active rest. The endurance protocol consisted of running at 75 to 85 percent of the lactate threshold for 45 to 75 minutes. Training time was matched with both training programs taking 2.5 hours total a week.
Results showed that the sprint interval group lost more body fat and more visceral belly fat than the endurance running group: The sprint group lost 1 kg of visceral fat and 2 kg of total body fat, while only losing 1 kg of lean mass. To put it in perspective, the sprint interval group lost 16 percent belly fat compared to the endurance running group that had no significant loss of visceral belly fat, but did lose 1 kg of total body fat and 1.4 kg of lean mass, producing a less favorable body composition.
In addition, the sprint training group had greater improvements in resting heart rate and peak oxygen uptake than the endurance training group, indicating greater cardiovascular benefits. Sprint training also improved running speed at the lactate threshold by 20.5 percent compared to only 12.9 percent in the endurance group. This was likely due to the fact that high-intensity training improved the use of fat for fuel, which leads to less glycogen being used for energy. Plus, being able to run faster with less exertion led to a much faster finish in the half-marathon time trial—the sprint group finished nearly three minutes faster than the endurance training group!
In terms of results, there’s no downside to high-intensity training since it provides greater fat loss, while sparing muscle. It elevates fat-burning hormones such as growth hormone, and it increases excess post-exercise oxygen consumption (the amount of energy burned in the 24 hours after exercise as the body recovers) much more than stead-state training. Plus, although this study matched training time with both groups exercising for 2.5 hours a week, other studies have shown that sprint intervals can produce better results than endurance exercise in less training time.
For example, one study found that a 23-minute sprint interval workout produced greater fat loss than a steady-state workout of 50 minutes. Another study compared a 20-week aerobic training program with a 15-week sprint training program (the training protocols took the same amount of time), and with five fewer weeks of training, the 15-week group lost more fat.
The only possible drawback to sprint training is that it is mentally challenging to push through an all-out workout even if it is short. The upside is that many trainees find intervals to be less boring than endurance training, and they enjoy feeling powerful and fast from going all out. Finally, the fact that the hard work you are doing will produce fat loss results is often enough to keep you going through a difficult, but short, workout.
Hottenrott, K., Sebastian, L., et al. Effects of High-Intensity Training and Continuous Endurance Training on Aerobic Capacity and Body Composition in Recreationally Active Runners. Journal of Sports Science and Medicine. 2012. 11, 483-488.
Tremblay, A., Simoneau, J., et al. Impact of Exercise Intensity on Body Fatness and Skeletal Muscle Metabolism. Metabolism. 1994. 43(7), 814-818.
Trapp, E., Chisholm, D., et al. The Effects of High-Intensity Intermittent Exercise Training on Fat Loss and Fasting Insulin Levels of Young Women. International Journal of Obesity. 2008. 32(4), 684-691.