I have been digging deep into lots of sprinting and interval training studies, and found some neat things. First, you can divide sprinting-type activities into three general categories:
- Aerobic Interval Training
- Anaerobic Interval Training
- Sprint Training
Aerobic interval training usually consists of longer intervals (2 min or more), and can be used to improve performance in distance events like a 5k race. Anaerobic interval training deals with shorter intervals and is more applicable to stop-and-go events like basketball or football. Sprint training consists of high-intensity sprints with long rest periods to recharge the muscles.
None of these types of training is inherently "better" than the others. They all can be used to improve performance in the appropriate events. But my interest is, which of these protocols is better for fat loss?
The first step is to look at this from an evolutionary perspective. Hunter-gatherers' physical activities were directed towards acquiring food. They did not "exercise" in the traditional sense - they were chasing after game (or occasionally being chased by it!). Hence, I was curious as to why hunter-gatherers (or other animals) would engage in something resembling "interval training".
I found some answers in this fascinating paper, "Metabolic Implications of a "Run Now, Pay Later" Strategy in Lizards". The paper begins by pointing out that the major energy expenditure with short, high-intensity efforts is in the calories burned after the exercise. The scientific name for this is "excess post-exercise oxygen consumption", or EPOC for short.
The paper then compares the total energy expenditure between short sprints when the rest periods are short or long. The authors find that there is a "metabolic savings" (less energy expenditure) when the pauses between the efforts are short.
In other words, let's say a person was going to perform 4 high-intensity, 20 second sprints. What would be the cheapest way metabolically to do this? The answer is to do them with little rest in between. This is because the longer the rest periods, the more calories are burned in EPOC while resting between sprints. If a person did them with only ten seconds rest between the sprints, the whole workout would be over in 2 minutes. Yet if a person put 10 minutes between each sprint, the person would get the full calorie afterburn or EPOC for each sprint. With both workouts you still get the after-workout calorie burn, but with the longer rest periods you also burn more calories during the workout.
