Workout Routines

Everything You Need to Know About HIIT

Maximize your fat-burning efficiency with high-intensity interval training.

by CSCS

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Setting Your Intervals

So how long do you have to perform each high-intensity interval to reap the benefits? Grinnell advises, “The most recent study, out of Australia, reported that a group of females who followed a 20-minute HIIT program consisting of eight-second sprints followed by 12 seconds of rest lost six times more body fat than a group that followed a 40-minute cardio program performed at a constant intensity of 60% of their max heart rate.” That’s three eight-second sprints a minute for 20 minutes. Very intense, but at least it’s over quickly.

A 1996 study by Japanese scientist Izumi Tabata gave rise to the now ubiquitous 20-on, 10-off Tabata protocol, which boosted conditioning in elite athletes. And University of Western Ontario researchers found that subjects who did four to six 30-second sprints with four minutes’ rest after each lost twice the fat of a steady-state group. Simple logic applies that the shorter the rest periods, the more intense the workout is.

The only catch to all this intensity is that it’s hard on the body. “You must change your workload frequently to avoid overtraining and burning out your central nervous system,” Grinnell says. “Sprinting is very demanding on both the brain and the body, so proper rest is important to maximize performance and results. The longer you sprint, the longer you need to rest.”

Bottom Line

The duration of your work and recovery bouts is important, but the name of the game is exertion. Keeping your sprints eight to 30 seconds long is adequate for stimulating fat loss. Recovery between intervals can vary but should be shortened as you become more acclimated to the demands of sprinting, to keep your body guessing (and leaning out).

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Workout Volume

No one can keep up a sprinter’s pace for very long periods of time, but intermittent bouts of recovery allow you to sprint multiple times in a given workout.

“The hormonal effect of sprinting is so dramatic that you don’t need endless sprints to increase fat loss,” says Grinnell. “The quality of sprints is much more important. HIIT requires great focus and energy demands. So if you’re able to perform at a high intensity for an extended period of time—much longer than 20 minutes—then you may not be doing it right.”

As to frequency, Grinnell says, “Two to three days per week is best for improving body composition and heart health.”

Bottom Line

The number of sprints performed is secondary to the quality of sprints performed. To make sure you’re able to maintain top speed throughout the session, perform as many sprints in the eight- to 30–second range as you can within 20 minutes.

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