High-intensity interval training is defined as repeated sessions of brief, intermittent exercise, often performed with an "all out" effort or at a high level of intensity.
This method of intense training may last from a few seconds to a few minutes, and it may include a number of repeats followed by a few minutes of rest or less intense exercise. The intense effort will increase skeletal muscle mass in activities such as running or cycling. It can also improve performance during an activity that relies on aerobic energy metabolism.
Such high-intensity intervals are intended to improve training strength. This type of exercise is less time consuming and can adapt to more prolonged periods of moderate-intensity exercise. For those who have time restrictions, you should only need to do intervals every other day, which means more days off. You will be able to reduce your training time, as well as the actual exercise strengthening, because of the higher intensity periods.