High-intensity interval training (HIIT), also called high-intensity intermittent exercise (HIIE) or sprint interval training (SIT), is a form of interval training, a cardiovascular exercise strategy alternating short periods of intense anaerobic exercise with less intense recovery periods. HIIT is the concept where one performs a short burst of high-intensity (or max-intensity) exercise followed by a brief low-intensity activity, repeatedly, until too exhausted to continue. Though there is no universal HIIT session duration, these intense workouts typically last under 30 minutes, with times varying based on a participant’s current fitness level. A typical 12 minute HIIT workout is equivalent to doing a 45-minute run.
HIIT workouts provide improved athletic capacity and condition as well as improved glucose metabolism. Compared with other regimens, HIIT may not be as effective for treating hyperlipidemia and obesity, or improving muscle and bone mass. However, research has shown that HIIT regimes successfully produced significant reductions in the fat mass of the whole-body. Some researchers also note that HIIT requires “an extremely high level of subject motivation” and question whether the general population could safely or practically tolerate the extreme nature of the exercise regimen.