High intensity interval training or HIIT is any cardio regime in which the heart rate is elevated to (close to) its maximum for a certain period of time and then decreased to a resting state. These cycles of high and low intensity training are repeated at regular intervals throughout the training session. The idea behind HIIT is that it is meant to increase the body’s threshold at which lactic acid is released in the muscles. This is beneficial as it is the release of lactic acid that causes the onset of failure at the end of a set during weight training. Therefore a lot of trainers prescribe interval training as a means of increasing this threshold and reaching new heights in muscle workouts.
There are many variations of HIIT, all of which change the length of time taken for the high and low intensity phases, as well as the overall time of the workout. For instance, Tabata is a type of high intensity interval training in which the intervals of high and low intensity are particularly short. Usually the high intensity workout phase lasts 20 seconds, followed by 10 seconds of rest. This is repeated for 4 minutes.
One advantage of interval training is that you don’t have to spend as much time to burn the same amount of calories as you would with regular flat heart rate cardio. HIIT can also increase your explosive power, your running speed and as already mentioned, it can increase your stamina in both cardio and weight training.
If you are training for an endurance event, such as a marathon or triathlon, you should not depend exclusively on HIIT to increase stamina. When training for endurance sports the best method is to practice with endurance cardio. This means longer periods of time spent at medium to medium-high heart rates. HIIT should form a part of this training, but your focus should be on flat heart rate cardio.