ones as well as longer, lower activity recovery periods and creates a greater homeostatic disturbance. Both HIIT and SIT fall into the larger class of interval training. Distinction between the two is not always maintained, even in academia: for example, Tabata describes his 170% VO2 max regimen as "supermaximal", but does not use the term SIT. Procedure HIIT exercise sessions generally consist of a warm-up period followed by repetitions of high-intensity exercises separated by medium intensity exercises for recovery, then a cool-down period. The high-intensity exercise should be done at near maximum intensity. The medium exercise should be about 50% intensity. The number of repetitions and length of each depends on the exercise, but maybe as little as three repetitions with just 20 seconds of intense exercise. The specific exercises performed during the high-intensity portions vary. Most of the research on HIIT has been done using a cycling ergometer, but other exercises like a rowing ergometer, running, stair climbing and uphill walking can also be effective. There is no specific formula for HIIT. Depending on one's level of cardiovascular development, the moderate-level intensity can be as slow as walking. A common formula involves a 2:1 ratio of work to recovery periods, for example, 30–40 seconds of hard sprinting alternated with 15–20 seconds of jogging or walking, repeated to failure. The entire HIIT session may last between four and 30 minutes, meaning that it is considered to be an excellent way to maximize a workout limited by time constraints. Use of a clock or timer is recommended to keep accurate times, the number of rounds, and intensity. An alternative form of HIIT, designed for heart rate training, involves a 30-minute period of cardio followed by 30 minutes of full-body resistance training to help maximize calorie burning. The idea is to combine aerobic exercise with intense weight and resistance training to achieve a high level heart rate for an extended period of time, in order to maximize strength and endurance. Branches Peter Coe regimen A type of high-intensity interval training with short recovery periods was used in the 1970s by the athletics coach Peter Coe when setting sessions for his son Sebastian Coe. Inspired by the principles propounded by the German coach and university professor Woldemar Gerschler and the Swedish physiologist Per-Olof Åstrand, Coe set sessions involving repeated fast 200 meter runs with only 30 seconds recovery between each fast run. Tabata