An additional factor, also discussed in the book is that there is often an increase…
The Growth Hormone Response to Interval Training – Q&A
Q: I just read your review of EPOC. Probably 16 years ago I read a study done at Laval U. It compared fat loss from steady exercise vs short bouts of intense exercise all done on a stat bike. Like the article, there was little difference in calorie burn between the two groups. But the intense group had significantly greater fat loss than the steady group. The researchers has no real answer as to why that happened. I wondered back then if it could be explained by the intense exercise stimulating growth hormone (GH). GH has a steroid-like effect on the body, accelerating fat loss among other effects.
A: I doubt it. GH is pretty irrelevant as an anabolic, studies have clearly shown that even injecting growth hormone (GH) does nothing to improve strength or muscle gains. So the small GH pulse from interval training is unlikely to explain the results of that original interval study. Rather, alterations in fat oxidation enzymes, muscle glycogen depletion, and the fact that, in untrained individuals, high intensity interval work can probably stimulate increases in muscle mass are more likely to explain the studies results. But GH is pretty worthless here.