HIIT — or high-intensity interval training — remains one of the most effective exercise methods known. Mixing brief bursts of high-intensity exercise with less-intense recovery periods boosts both aerobic and anaerobic fitness.
You can do HIIT with almost any type of cardiovascular exercise: running, cycling, swimming, inline skating, jump roping and so on. Build your program around four to 10 high-intensity intervals of at least 30 seconds. Separate the intervals with recovery periods of one to two times as long as the high-intensity intervals. So if your high-intensity intervals are 90 seconds long, your rest periods might be anywhere from 90 seconds to 180 seconds, or three minutes long.
Don't worry, you don't have to jump right into a super-intense workout — in fact, you really shouldn't. Your body needs time to adapt to the demands you're about to put on it, so gradually ease into the workout with a five to 10-minute warm up. Then do a five to 10-minute cool down after the workout, to ease your body back to a state of rest. Both warm up and cool down should be gentler versions of the workout you're about to do. So if you're going to be running, you would warm up by walking or jogging.
Elite athletes who use this training method have access to all sorts of technology to monitor their intensity levels. For most casual exercisers, it's easiest to monitor activity with ratings of perceived exertion, or RPE. RPE is simply your own perception of how hard you're working out on a scale of 0 to 10, where 0 is sitting at rest and 10 is maximal effort.
Your warm up and cool down should be about a two to a four on that subjective scale. Your high-intensity intervals won't quite hit maximal effort — they should be a seven to nine — and your recovery intervals will be somewhere in between those two extremes. Note that if you keep doing the same workout over and over, it's going to start seeming easier; once you notice your ratings of perceived exertion declining, you can transition to a more challenging HIIT program.
