Though interval-type exercises have been around for more than a half a century, the last decade has witnessed an explosion of interest by researchers and people wanting to get in better shape.

Research started with protocols that required participants to pedal at an all-out intensity for 30 seconds before recovering for a few minutes and then doing it again and again several more times.

Then came relatively long but less intense intervals in cardiac patients.

Findings from these studies found interval-based exercise to be a powerful tool for improving exercise performance and health.

This form of training is so flexible, it has produced an endless number of training options and several different names to describe it: high-intensity interval training, sprint interval training, or high-intensity interval exercise.

One other aspect relates to the style of exercise. Most workouts focused on using traditional cardio-based exercise options such as running and cycling.

However, much of the contemporary use of high-intensity interval training includes some combination of resistance exercise and calisthenics. Most of the research point towards both forms being highly beneficial.

The important idea behind all forms of this kind of training is providing an intense phase of exercise followed by a period of recovery.

Each phase can range from a few seconds to a few minutes and are conducted across a range of intensities. The number of ways it can be configured is numerous.

High-intensity interval training provides the extra benefits of intense exercise without creating a negative or unpleasant experience.

While there is no magic recipe, research suggests avoiding work intervals that are both long and extremely intense. Longer intervals should be paired with high intensities, while shorter intervals can be paired with very high intensities.

Source: American College of Sports Medicine: acsm.org