Fitness: Has high-intensity interval training been oversold?

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High-intensity interval training (HIIT) ranked first in the American College of Sports Medicine’s annual Global Survey of Fitness Trends for the first time in 2014 and has remained in the top 10 since then. It’s the darling of the fitness world, and there seems to be little HIIT can’t do.

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Characterized by short bursts of high-intensity exercise (between one and four minutes) followed by short periods of rest, HIIT’s popularity lies largely in its ability to deliver big results in a short time. The health and fitness benefits have been shown to be similar to or better than moderate-intensity workouts that take twice as long.

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It’s not just the gym crowd that has been crowing about HIIT. The research community has been bringing young, old, fit, unfit and everyone in between to the lab to see if the magic of HIIT is universal. In general, it is. Most of the populations studied have benefited from significant improvements in health and fitness. But what’s still up for debate is whether athletes find high-energy workouts more enjoyable than consistent, moderate-intensity exercise.

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Panteleimon Ekkekakis, Professor and President in the department of kinesiology at Michigan State University, he has spent most of his career studying how different intensities of exercise make people feel. She has been following the HIIT trend since news of its benefits began circulating among exercise physiologists in the early 2000s.

“HIIT started to gain traction at an amazing rate and became this huge global phenomenon,” said Ekkekakis, who says there are about 700 studies published a year on HIIT.

In the early days, HIIT was considered more appropriate for athletes and very fit people, but it wasn’t long before fitness experts suggested it might prove valuable to the average Joe and Jill. Exercise psychologists like Ekkekakis had their doubts.

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“It’s never going to work, because we all know that high-intensity exercise sucks,” he said.

To reap the vaunted benefits of HIIT workouts, you need to train at 85 to 95 percent of your maximum effort (maximum heart rate), which isn’t for everyone. The no pain, no gain exercise philosophy has always been embraced by the few, not the masses. Despite this, researchers began to publish data suggesting that HIIT is not only well tolerated by average exercisers, but is actually enjoyed more than less intense workouts.

The combination of enjoyment with the promise of significant results in less time is the holy grail in terms of exercise adherence. Lack of time has been cited as one of the main reasons why few people exercise regularly.

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Still, Ekkekakis wasn’t buying it.

“It’s much more complicated than that,” he said of why the dropout rate from exercise is so high. “Most people have discretionary time, they just choose not to allocate that discretionary time to exercise, presumably because they find other things that make them feel better or give them more satisfaction.”

Citing a preponderance of evidence showing that intensity turns people off, Ekkekakis decided to take a closer look at HIIT’s track record for long-term adherence. the The results were published in a recent issue of Psychology of Sport and Exercise.. Along with his colleague Stuart Biddle of the University of Southern Queensland, Australia, Ekkekakis identified eight quality studies comparing HIIT to moderate-intensity exercise, all of which included follow-ups of at least 12 months. What they found is unlikely to make HIIT fans happy.

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“While non-adherence and drop-out represent major challenges for any form of exercise, especially in unsupervised settings, these problems have been shown to be exacerbated by HIIT,” Ekkekakis and Biddle said in the study. “Compared to moderate-intensity exercise, more people assigned to HIIT failed to adhere to their prescription when unsupervised, most likely because they couldn’t.”

Not all of the study subjects gave up exercise altogether, some just weren’t as motivated to maintain the same intensity on their own as they were under the watchful eye of an instructor. They reduced the workouts one or two levels to a more comfortable moderate-intensity range. That’s not a bad thing, it’s just that when combined with the short duration of most prescribed HIIT workouts, the health and fitness benefits are likely to be less significant than advertised.

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So where does the idea come from that athletes prefer HIIT to less intense workouts if all eight studies showed that most people eventually ditched HIIT altogether?

It turns out that measuring exercise enjoyment is harder than you think. People are not in a position to answer questions about how they feel in the middle of a hard workout. Any queries should wait until the training is over. With all the hard work done and most people feeling accomplished with their efforts, their feelings are very different than when they were in sweat mode.

“After exercise, almost everyone feels fine,” Ekkekakis agreed. “But they can feel good because the damn thing is already done.”

Does that mean that HIIT has been oversold as a solution to sedentary habits? Probably. But that doesn’t make it a bad option. It’s just not for everyone, which puts it on par with most other workouts. The indicator of effective training is not how successful you are in a lab, but whether you want to do it all over again on your own.