Among the people at your gym steadily spinning their wheels on the cardio machines, there's always that one loud, sweaty psychopath. He sets the treadmill to maximum speed and pounds out sprints for 20 seconds, rest, then repeats. She's a bullet from a gun on the spin bike or elliptical—all flailing arms, legs, and ponytail—until after 30 seconds, when she reloads and repeats. Hardcore gym goers love this method of sprint-and-stop training, high-intensity intervals, and fitness gurus claim it has unique benefits over steady-state cardio. But a new study suggests that isn't so.
High-intensity interval cardio doesn't burn any more fat than traditional cardio, according to new research in Obesity Reviews. That's what scientists determined after they analyzed 31 studies on the topic and found the two methods resulted in the same fat loss. This goes against the longstanding notion that high-intensity intervals may burn more fat, in part because of what scientists call excess post-oxygen consumption, also known as EPOC, a phenomenon where your body uses extra energy after your workout to restore your body from the harder effort.
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The scientists compared three different methods: steady state cardio, done for 20 to 60 minutes at about 65 percent of maximum effort; high-intensity interval training, cardio in one-to-four-minute spurts at about 80 percent of max effort; and sprint intervals, done in 8-to-30-second bursts at an all-out effort. When the scientists matched the methods for how much energy each burned—for example, a 30-minute, slower bike ride that burned 500 calories compared to 15 minutes of bike intervals that also burned 500 calories—they discovered that participants lost equivalent amounts of fat.
"I thought that intervals may confer a slight advantage, but it wasn't terribly shocking they didn't," says Brad Schoenfeld, an exercise researcher at Lehman College. "The basis of weight loss is calories in, calories out. So if you're expending a similar amount of energy in an exercise session, you'd figure there would be roughly equal effects on fat loss."
Interestingly, neither of the three methods resulted in meaningful weight loss, according to the researchers. "Cardio in general just isn't a great way to lose fat," Schoenfeld says. "Fat loss is primarily mediated by diet. Eating less is how you can more easily affect large caloric differences." Cardio alone only creates big caloric reductions if you're doing massive amounts of it.
That's not to say you should skip your workout and just eat less. Regular exercise can reduce your health risks, improve your mood, and even help you live longer, according to the Mayo Clinic. A unique benefit of intervals is that they deliver many of those health benefits in less time, according to researchers at McMaster University. And research from the National Weight Control Registry shows that 94 percent of people who've lost more than 30 pounds and kept it off increased their physical activity. Ninety-eight percent of those people also altered their diet.
Pat Davidson, a New York City-based exercise physiologist, worries that people will learn about the new study and use it as a result to avoid uncomfortable exercise. "At a certain point, exercise is just a math equation," he says. "Most people train just a few hours a week. The one thing we've learned from CrossFit is if you exercise with intensity and you try really, really hard, you will see your body change. As long as the number of calories you're eating stays constant, if you do more work, you'll see better results."
Recently, workouts as short as four minutes have gained popularity. If you are attempting to create a calorie deficit with exercise, that probably won't be enough. By sprinting for a total of four minutes, for example, a 130-pound woman would burn 93 calories. She'd burn about 350 running for 30 minutes. "It's often a question of how much time you have," Davidson says. "Whatever that number is, just work hard."
While this study found the EPOC effect of cardio to be minimal, previous research has shown that weight lifting does result in an EPOC effect. Might there be a larger after burn effect doing weight-based intervals compared to a classic weightlifting routine? "I haven't seen that topic adequately studied, so I can't say," Schoenfeld says. "But in theory, I highly doubt it because the primary effect of resistance training on EPOC is from increased muscle protein remodeling, and there's no evidence weight-based circuit training would have a greater effect than a traditional weight routine in that regard."
If you're an athlete, intervals may help you perform better. Consider the principle of specificity, which states that to become better at a physical skill, you must perform that skill. If you play a sport that has a lot of short bursts of running followed by walking or jogging—like in basketball or soccer—Schoenfeld says you'd likely want to include intervals in your fitness program.
How should you take this advice to the gym? "Just do whatever form of exercise you'll do most often," Shoenfeld says. "Because adherence is the most important part of any program."
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