Short, high intensity exercise can take many forms, but it has certain constants—the exercise will be purely anaerobic in its nature (usually activities or individual segments of a longer exercise of fewer than 90 seconds duration), and it will require the athlete to perform at between 75% and 85% of the maximum physical capability.
Short, high intensity exercise can be the component of a longer and otherwise aerobic program; running high speed intervals in the middle of a longer slower run is a common example. Common short, high intensity exercise will include sprinting, weight-lifting, and the traditional field athletics such as the shotput, hammer throw, high jump, and discus. In each case, there is a very large expenditure of energy within the short time period. The intense effort required of the athlete is also highly focused toward the athletic goal, with very little extraneous effort. For this reason, short, high intensity exercise activities tend to be ones where technique, economy of movement, and execution are as important as the energy that the body is able to generate to complete the physical actions involved.
Short, high intensity exercise has a number of physiological attractions to the recreational athlete who is interested in fitness and weight loss, as these activities tend to require the body to expend a greater number of calories than medium or low intensity pursuits. The average adult person who runs three miles at a rate of eight minutes per mile will expect to expend approximately 300 calories; the same person who runs the same distance over the same terrain at a pace of 6.5 minutes per mile will expect to expend 350 calories. There is also a greater benefit derived by the athlete after the workout is concluded; high intensity exercise provides a greater boost to the metabolic rate for up to 24 hours after the activity is completed, where the corresponding low or medium intensity exercise creates a negligible difference in metabolic rate. For short, high intensity exercise that is added as a component to an ongoing fitness program, the athlete can expect overall body fat to be reduced by between 3% to 5% over a six-month period, assuming that there are no other variables.
The other crucial benefits of short, high intensity training are the improvement of the person's VO2max, the measure of the ability to process oxygen, and a generally greater strength built throughout the musculoskeletal system. The resistance inherent in short, high intensity exercise that is directed to the body will both build muscular strength and prevent bone density reduction.
Most short, high intensity exercises place significant emphasis on explosive movement at some point in the activity. Success in these disciplines will ultimately involve the specific training of the fast-twitch fibers in the target muscle groups. Plyometrics is the type of training engaged to enhance fast-twitch muscle response and to generally develop an explosive ability that may be sustained throughout the duration of the exercise.
The relative brevity of the exercise requires the athlete to pay even greater attention to the warm up/cool down cycle. A warm up will permit both the musculoskeletal system and the cardiovascular system to be brought to the operational status necessary to work at the body's maximum rate; stretching and flexibility components to the warm up that address the muscle groups to be used at high intensity tend to reduce injury by as much as 50%. Cool down serves to gently reduce the body's heart and respiration rates, while keeping the muscles loose.
Short, high intensity exercise is sometimes viewed as a weight loss panacea by persons with poor fitness who wish to lose weight. Such persons are at significantly greater risk of injury as short, high intensity exercise, by its nature, places demands on the body to which an unfit person will be unaccustomed. Unless the person possesses excellent fitness, short, high intensity exercises or training must be approached incrementally.