HIIT It and Quit It


Facebook is excellent for keeping tabs on old friends — and ex-boyfriends — but it’s not always ideal for getting sage advice. However, when a friend posted the above question on my Facebook page, I actually did have an answer for her: Skinny Dude needs to either keep up with the research or mind his own business.

Over the last 20 years, scads of studies have shown high-intensity interval training to be more effective at burning fat and preserving — or even building — lean muscle mass than steady-state cardio sessions. Consider just a few of the findings:

• In 2001, East Tennessee State University researchers found that over eight weeks, the HIIT group lost 2 percent body fat; those performing steady-state cardio lost none.
• Australian researchers found that women doing a 20-minute HIIT program of eight-second sprints followed by 12 seconds of rest lost six times more body fat than women doing 40 minutes of steady-state cardio at 60 percent of their maximum heart rate.
• In 2007, a group of Canadian researchers found that women who did seven HIIT workouts over two weeks saw their fat oxidation — and the levels of muscle enzymes that enhance it — increase by 30 percent.

Serious gym rats have long known that weight training increases resting metabolism for up to 24 hours after a lifting session. HIIT works exactly the same way. So not only will it not burn your hard-earned muscle, but it also may even help you build some: One study has revealed that men following a six-week HIIT program for 15 minutes a day gained an average of 2 pounds of muscle apiece, despite doing nothing but cardio during the trial.

How does it work? Think of it this way: If you pick up a 5-pound weight and curl it for 30 minutes straight, you’re not going to build much muscle because you’re not providing enough resistance; that’s what you’re doing during steady-state cardio. But if you use a heavier weight and then stop and start again and then stop and start again, well, now you’re giving resistance and approaching failure, both of which provoke the muscle to grow. That’s what HIIT does. By pushing your body to run as fast as it can, you increase the resistance placed on muscles while you’re sprinting and make them work harder to reverse that momentum when it’s time to stop. HIIT basically applies what works in weight training to cardio.

This is not the approach my Facebook friend takes. She does intervals — alternating periods of higher-intensity work with active or complete rest — but spends an entire hour on the recumbent bike, starting out with relatively light resistance and cranking it up a notch with each work interval. Midway through, it starts getting intense; by the end, she’s cooked. Is there anything wrong with that approach? Not if you’re working fairly hard for the majority of the time, and you’re actually lucky enough to have an entire hour to devote to cardio — and want to. But if you can get even better results in 20 to 30 minutes by working at 90 percent of your maximum heart rate the entire time, why would you want to spend an entire hour doing cardio?

The research is clear: If you want the small, stringy muscles of a marathon runner, all you have to do is train like one — spending lots of time with your heart rate relatively low. But if you want to be lean and muscular, HIIT it, quit it — and move on.

And for the record: Skinny Dude still needs to mind his own business at the gym.

“This guy comes up to me at the end of my hour on the bike and tells me I need to bike so that my heart rate is at 115 to 120 the whole time. And that fat is burned at 115, carbs at higher heart rates. I’ve had lots of people recommend intervals to me. What say you?”