Sprint Interval Training - “It's a HIIT - Strength Coach.com

work out time, one would want to be utilizing fat as the fuel of choice during this period to stay lean; SIT and HIIT
accomplishes this very well. It is interesting to note that, for a single bout of maximal exercise, it has been shown
that sixty seconds is optimal to maximize EPOC 68 . The reason for this finding is fairly straightforward. It is at the
60‐second mark of an all out effort that humans accumulate the highest levels of lactic acid, which, in turn, inhibits
further high‐intensity muscle contraction and the anaerobic production of more lactic acid. And, the amount of
lactic acid produced during exercise is highly correlated with the magnitude of EPOC because much of the elevated
oxygen consumption is for the processing of the lactic acid. It has also been shown that compared to one
continuous bout of exercise, the magnitude of EPOC is significantly elevated by splitting the equivalent exercise
into two sessions 69 , supporting the benefits of interval training when the aim is to increase overall energy
expenditure. Based upon this finding, it perhaps should not be surprising that prescribing exercise in several short
bouts versus one long‐bout per day produced similar changes in cardiorespiratory fitness and had a trend toward
greater weight loss 70 . It has further been demonstrated that following high‐intensity exercise, but not low‐
intensity exercise, oxygen consumption remains elevated above resting levels at three hours post‐exercise; further,
at this 3‐hour time point, the rate of fat oxidation was higher after high‐intensity exercise as compared to low‐
intensity exercise 71 .
As it turns out, the lactic acid produced from high‐intensity anaerobic exercise is more than the waste
product it was once thought to be. It is used as a fuel, a buffering aid and, of immense importance, a likely
signaling molecule 72‐74 . At high levels, lactic acid is correlated with powerful anabolic metabolites such as
testosterone and human growth hormone (HGH) 75‐77 , which further direct metabolism toward a strong and lean
physiology. Both EPOC and these hormonal messengers persist long after the exercise has ended, which helps
explain why SIT is more effective for fat loss than LMICT, despite when sometimes having a lower caloric
expenditure than a LMICT session 78‐80 . When considering the effect of exercise on body composition, one also has
to realize how hormones work when alone or in the presence of other hormones. Both HIIT and LMICT produce
cortisol which, when alone, can be catabolic to the body as well as decrease lipolysis and, along with insulin,
facilitate lipid accumulation by expressing lipoprotein lipase (LPL) 81, 82 . However, unlike with LMICT, the increases
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