HIIT is a form of cardiovascular exercise that alternates short periods of intense anaerobic exercise with less intense recovery periods. These short, intense workouts provide greater athletic ability and condition, accelerates the metabolism and produce greater fat burning.
It's a short duration training (about 20 minutes) and high intensity. To perform it you must alternate short peaks of very high effort (above the 90% of our maximum heart or FCM) with longer recoveries at a moderate pace (around 60% of our FCM).
When HIIT is more useful? Especially in stages of muscle definition in which we want to lose fat without sacrificing the muscle that we have won in the muscle bulking period, since this type of training preserves muscle mass.
It is very effective to further enable our metabolism, even after completing the exercise.
In HIIT the really interesting thing is that any type of exercise can be done: run, treadmill, bike, eliptic machines, plyometrics, squats, squatting, bending, planks, bench press, biceps curl, pull-ups, push-ups, deadlifts, quadriceps extensions. In the gym with weights, machines, body weight, elastic bands... the possibilities are endless!
HIIT works because burning fat requires oxygen and the more oxygen that gets inside your body, the more fat your body burns. A high-intensity workout increases your body’s need for oxygen during the effort and creates an oxygen shortage, causing your body to ask for more oxygen during recovery. This “afterburn” effect is referred to as excess post-exercise oxygen consumption (EPOC) and is the reason why intense exercise will help burn more fat and calories than regular aerobic and steady-state workouts.
So, one of the awesome effects of all that hard work from HIIT is that it will kick your body’s repair cycle into hyperdrive, meaning you will actually continue to burn fat for 24-48 hours after interval training, not just during your workout.
But hold on, because you need a good aerobic base to do it safely: HIIT is not for everyone because there can be: orthopedic, cardiac and even psychological reasons to avoid HIIT.
If you are looking for weight loss, the best will always be to perform HIIT (as long as you have the level required to perform it) along with weight training (either with your bodyweight or training with weights that I detail in my Weights section) and a good nutrition is also mandatory (see my Nutrition section).