High intensity interval training, hereafter called HIIT, is a great exercise for people who are maxing out in their workouts but are not increasing their muscle mass. One of the reasons that exercises will hit plateaus is because they are doing the wrong type of exercises.
In some instances, the exerciser should cut out exercising for as long as three weeks and let the body systems that have been taxed to the max catch up to the enlarged muscles that they have been fueling. If this is the needed step for an exerciser it should be taken seriously; total rest is the prescription, not low intensity exercise with low reps.
For everyone else, however, the answer will likely be to try out a different type of exercise. HIIT is different from any other form of exercise that will offer you both aerobic and anaerobic benefits.
At their core, HIIT regimens are built on aerobic exercises such as running or exercise bikes. Running on a treadmill could also work for HIIT, but the need to change quickly between high speeds and low speeds makes anything but an extremely programmable treadmill a difficult option. In the same way, riding a bike outside could also thwart your attempts to use HIIT unless you have a large and unobscured stretch of road that you can really let loose on.
The most effective HIIT regimen uses 20 second burst of power sprints followed by 10 seconds of rest or low intensity exercise such as a walk or a slow pedal. If this regimen is observed for four weeks or more, the exerciser will begin to see benefits that are similar to steady aerobic exercises along with the additional benefits of anaerobic fitness.