HIIT is not “anaerobic” exercise

Interval training is not “anaerobic” exercise

Interval training is frequently (mis-)characterized as “anaerobic” exercise. The reality is that repeated sprints are mainly fuelled by aerobic (oxidative) metabolism. Figure 7 from this classic study in The American Journal of Physiology (full article here) shows energy provision during a series of 30-second ‘all out’ cycle sprints. The contribution from anaerobic metabolism declines over repeated bouts of intense exercise. This is mainly due to an impaired capacity to break down muscle glycogen. In contrast, aerobic metabolism increases over time and it becomes the dominant energy source.