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 fitness trends survey for the first time in 2014 and has remained in the top 10 ever since. It’s the darling of the fitness world, and there seems to be little that HIIT doesn’t can.

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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 largely lies in its ability to produce big results in a short amount of time. Health and fitness benefits have been shown to be similar or better than moderate-intensity workouts that last twice as long.

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It’s not just studio audiences who are raving about HIIT. The research community has brought the young, old, fit, unfit and everyone in between to the lab to see if the magic of HIIT is universal. Broadly speaking, it is. Most of the populations studied have benefited from significant gains in health and fitness. But what’s still up for debate is whether lifters find high-energy workouts more enjoyable than moderate-intensity steady-state training.

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Panteleimon Ekkekakis, Professor and Chairman in the Department of Kinesiology at Michigan State University, has spent most of his career studying how people feel during different intensities of physical activity. He’s been following the HIIT trend since news of its benefits circulated among exercise physiologists in the early 2000s.

“HIIT started taking off at an amazing rate and has become this huge global phenomenon,” said Ekkekakis, who claims there are about 700 published studies on HIIT annually.

In the early days, HIIT was considered more suitable for athletes and very fit people, but it wasn’t long before fitness experts suggested it could prove valuable for the average Joe and Jill. Sports psychologists like Ekkekakis were skeptical.

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

To reap the much-touted benefits of HIIT training, you need to train at 85 to 95 percent of your maximum exertion (peak heart rate), which isn’t for everyone. The no-pain-no-gain philosophy of training has always been embraced by the few, not the crowd. Despite this, researchers began publishing data suggesting that not only is HIIT well tolerated by the average lifter, but that they actually find it more comfortable than less intense workouts.

Combining enjoyment with the promise of significant results in less time is the holy grail of exercise compliance. Lack of time was cited as one of the main reasons why so few people exercise regularly.

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Still, Ekkekakis didn’t buy it.

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

Citing an overwhelming body of evidence showing that intensity drives people away, Ekkekakis decided to take a closer look at HIIT’s track record for long-term adherence. The findings were published in a recent issue of Psychology of Sport and Exercise. Together with his colleague Stuart Biddle from the University of Southern Queensland, Australia, Ekkekakis identified eight quality studies comparing moderate-intensity HIIT, all of which included at least 12 months of follow-up. What they found probably won’t make HIIT fans happy.

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“While non-compliance and dropout are major challenges for any form of exercise, especially in unsupervised settings, these issues have been shown to worsen with HIIT,” Ekkekakis and Biddle explained in the study. “Compared to moderate-intensity exercise, more people assigned to HIIT didn’t follow their prescription when unsupervised, most likely because they couldn’t.”

Not all study participants gave up training completely—some just weren’t as motivated to maintain the same intensity on their own as when they were under a trainer’s watchful eye. They took the workouts down a notch or two to a more comfortable, moderate-intensity range. That’s not a bad thing – it’s just that the health and fitness benefits combined with the short duration of most prescribed HIIT workouts are probably less significant than advertised.

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So where did the idea that lifters preferred HIIT over less intense workouts come from when all eight studies showed that the majority of people eventually gave up HIIT altogether?

It turns out that gauging the fun of working out is harder than you might think. People are unable to answer questions about how they feel in the middle of a hard workout. All requests must wait until after the training. With all the hard work and feeling that most people feel fulfilled in their efforts, their feelings are very different than when they are in full sweat mode.

“After training, almost everyone feels good,” agreed Ekkekakis. “But they might feel good because the damn thing is done.”

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