HIIT: Your Fast, Fat-Burning Workout

Blast more fat but work out less: It may sound like a bogus infomercial claim, but dozens of scientific studies support the timesaving, calorie-zapping benefits of quickie workouts known as high-intensity interval training (HIIT).

There’s good reason why HIIT is one of the hottest workouts around: Its format – brief bouts of hard exercise paired with easier activity for recovery – burns off more calories per minute than doing a longer workout at a continuously moderate pace. And researchers at the University of Guelph found that women who trained with high-intensity intervals for two weeks increased their bodies’ capacity to burn fat while they exercised. HIIT also makes the heart grow stronger; a study from Medicine & Science in Sports & Exercise showed that high-intensity intervals may be better for improving cardiovascular fitness in healthy adults than moderate steady-state exercise.

What makes HIIT work so well? One factor is the type of muscle fibers used. “HIIT recruits large, powerful muscle fibers that otherwise lie dormant in everyday life or during moderate exercise,” says Martin Gibala, PhD, a professor in the department of Kinesiology at McMaster University in Hamilton, Ontario, Canada. The training perk? Faster fitness gains, including more noticeably defined muscles.

And the benefits aren’t all physical, either. HIIT can help you dodge de-motivating workout ruts. “There are only so many ways to run for an hour on a treadmill,” says Gibala. “Interval training provides infinite variety, and it’s fun.”

Ready to give HIIT a try? With the right approach, practically anyone can benefit from this calorie-incinerating cardio workout. Read on for more of Oxygen’s myth-busting truths about HITT. Then dial up your next workout using our downloadable workout (at left) for a stronger, leaner body in no time.

HIIT Myth: It has to be “all-out” to be effective

Research subjects who do high-intensity interval training often work out at or close to their all-out capacity, but the average person can modify as needed. Gibala says effective interval training simply involves scaling the workout to your level of fitness and capabilities. “The goal is to take brief excursions out of your comfort zone,” he says.

What’s your comfort zone? Think of it as the feeling you get doing a moderately paced 30-minute bike ride or jog – it’s challenging but not super intense. HIIT requires you to kick that feeling up a notch for anywhere from 10 seconds to a couple of minutes at a time.

While there’s no reason to push yourself to the point of exhaustion, your work intervals should qualify as pretty tough, says Pete McCall, MS, an exercise physiologist with the American Council on Exercise in San Diego, California. “Work intervals should feel extremely challenging and be at an intensity that can only be maintained for a short period,” he says. You can nail down the right intensity by paying attention to how you’re breathing and talking: During work intervals, you should be breathing quickly and only be able to speak a few words at a time. As you recover, your breathing should return to normal so you can speak in full sentences again. (Download your rate of perceived exertion scale, above left, for more information.)

Also keep in mind that the recovery phase is just as important as the work phase. “Real fitness is identified by how quickly you can recover and not simply by how hard you can work,” McCall explains.

HIIT Myth: Interval training is only for the super-fit

If you’re at an intermediate level of fitness, you can still benefit from interval training, but heed this advice from McCall: To avoid injury and boost your overall success, kick off HIIT with moderate-intensity work intervals, gradually ramping up intensity over eight to 12 weeks, with two to three weekly workouts. “This allows your body to adapt to the demands of HIIT,” he says.

As an example, McCall suggests jogging for three to five minutes (work interval) then walking for three to five minutes (recovery) as your initial interval pattern. Gradually increase your running intensity during the work interval as you also progress from walking to jogging during the recovery interval.

HIIT Myth: You need to do HIIT for longer than 30 minutes for it work

The beauty of HIIT is its time efficiency – HIIT provides a lot of bang for your workout buck, so you don’t need to go for as long as you would at a lighter pace. In fact, a study by Gibala and his colleagues at McMaster University found that subjects who exercised for up to nine minutes a week for two weeks showed similar increases in endurance compared to those who sweated it out for five hours a week. Less than 10 minutes for a complete cardio workout sounds ideal, but you probably guessed there’s a catch: The study participants exercised as hard as they could for bouts of 30 seconds, with four minutes of rest between intervals. Going full-force is tough for even the most dedicated fitness fan to tolerate, so experts suggest gearing up to a slightly lower rate, around seven to nine on the RPE scale.

HIIT Myth: You need a cardio machine to get results

You can do HIIT almost anywhere: On an outdoor running track, in your garage with a jump rope or on your favorite cardio machine at the gym. One caveat: If you’re worried about stress to your joints, Gibala recommends activities like cycling and swimming over high-impact running.

HIIT Myth: You’re only burning calories during your workout

Studies show that HIIT is efficient at blasting fat and calories because of what happens both during exercise and after it: The more intensely you exercise, the more calories your body burns later. McCall explains that’s because high-intensity intervals require more oxygen for your body to recover after exercise, adding, “This effect from a HIIT session can last hours post-exercise while the effect from a steady-state training session may last only minutes.”

HIIT Myth: HITT should take the place of your other cardio workouts

With all the benefits of high-intensity interval training, you might wonder if it’s time to ditch your other cardio workouts in favor of an exclusive HIIT regimen. Not so fast, say the experts. Use HIIT for crosstraining, not as a replacement for all cardio. “It’s not an either/or proposition,” says Gibala. The best approach is to weave HIIT into your existing schedule as a way to rev up fat loss and fitness gains. And keep in mind it’s possible to get too much of a good thing – that’s where the risk of overtraining lies. “HIIT should not occur on a daily basis,” says McCall.“Do it two to three times a week with at least 48 hours of recovery between training sessions.” Avoid skipping workouts between HIIT days though. “Instead,” says McCall, “participate in lower-intensity workouts following a HIIT session.”