There are two parts to the science of anaerobic high intensity training (HIT) we need to know. First, the essential physiological factors and secondly, what training equipment can accommodate them.
Physiologically the exercise “effort” must be maximal, like an all out sprint. This is essential to engage the fast-twitch muscle fibers at the Maximum Power Level in order to exhaust the ATP-PC System in the first 11 to 13 seconds of the workout. This “full sprint effort” must continue to exhaust the Glycolytic System, creating a serious oxygen debt while accumulating huge amounts of lactic acid. When lactic acid can not be removed quickly enough by the overwhelmed cardiovascular system, the brain is signaled that there is some serious work going on for which more muscle is essential. In response, the pituitary gland orders human growth hormone production, which gets distributed throughout the body. To remove the accumulated lactic acid and deliver glucose and oxygen, the cardiovascular system works at full capacity. Ultimately, the greater the lactic acid concentration the greater the training effect for both the cardiovascular system as well as the participating muscular system.
Also, it is essential that the high intensity training involves a sufficiently large fast-twitch muscle fiber mass, in order to challenge the cardiovascular system. For most the muscle mass of the legs, with large muscles, like Gluteus Maximus (gluts), is ideal for reaching the optimum training effect with high intensity training (HIT). In the event the participating muscle mass is too small, the training effect becomes local, rather than overall beneficial.