In 2009, New York Times writer Gretchen Reynolds discovered something big: Readers loved to click on stories about tiny increments of exercise. That June, Reynolds wrote her first story about single-digit high-intensity interval training, or HIIT. The piece, titled “Can You Get Fit in Six Minutes a Week?,” described a study from Martin Gibala, professor of kinesiology at McMaster University in Ontario, Canada, on the effects of stationary biking.
The premise of the experiment was simple. Gibala had divided college students into two groups—one that exercised on the bike at a “sustainable pace” for up to two hours, and another that did so for just a few minutes at “the highest intensity the riders could stand.” After two weeks of exercising three times a week, both groups showed roughly equivalent increases in endurance. “In other words,” Reynolds wrote, “six minutes or so a week of hard exercise … had proven to be as good as multiple hours of working out.”
To Reynolds’ surprise, the initial piece was “hugely popular,” she recently told me over the phone from her home in New Mexico. She’s been writing about similar studies ever since. Avid New York Times readers may also be familiar with the most famous entry, the seven-minute full body exercise (which the newspaper spun out in 2014 into its own app), or more recent additions, like the four-second aerobic interval and three-second strength exercise (which qualifies as the shortest example to date). Despite her prolific output, Reynolds is choosy—these stories, each a traffic bonanza, represent just a fraction of the actual research on shrinking workouts. “There are dozens of studies that are coming out every week,” she says. (She is also careful to clarify that, though she wrote the story that inspired it, she had no involvement in the seven-minute workout app’s development.) Whether they’re called “minimalist workouts,” sprint interval training, one flavor of “exercise snack,” or—my personal favorite—micro-HIIT, forms of minimal-input, maximum-reward exercise have been all the rage for more than a decade. But it’s unclear how beneficial these exercises are—or who’s participating.
Interval training is nothing new. “We tend to rediscover the power of intervals or intermittent exercise every decade or so,” Gibala, the kinesiology researcher, tells me. Athletes have been using similar methods for at least a century. Paavo Nurmi, the nine-time Olympic Gold medalist, trained in part by running 60-second intervals 20 times with short rest periods in between. In the 1950s, the Royal Canadian Air Force devised a program called 5BX, or “Five Basic Exercises,” essentially a full-body workout designed to be completed in 11 to 12 minutes. All that’s really changed is that today’s intervals are both smaller and more prominent than ever, offered to us in Peloton classes (where you might do many short repetitions on a bike or treadmill over 20 or 30 minutes) and the pages of the New York Times (ideally in increments you could do between Zoom calls).
Scientists are still sussing out the benefits of micro-HIIT for the average person. Though Reynolds’ work invites the reader to try out one tiny workout or another for themselves, in a way she’s really just covering the steady march of research as scientists test various theories and share the results in journals. Early coverage led many readers to experience a sense of relief. In an era where many people felt a “real” workout requires blocking out an hour on the calendar each day, “the idea that this very short amount of exercise was still good was so freeing,” says Anna Maltby, a Brooklyn-based editorial consultant and certified fitness trainer. But these ever-shorter intervals could be seen in a more negative light too. “It has a strong diet culture scent to it for me,” Maltby added. “It’s like any of those gizmos or other products that promise maximal results with minimal effort, and it’s very appealing and marketable, but ultimately not sustainable—whether because it leads to injury or because it just isn’t fun for people.”
A growing body of evidence seems to support this skepticism, says Panteleimon Ekkekakis, a professor of exercise psychology at Iowa State University and an outspoken critic of HIIT. (Reynolds herself recommended Ekkekakis as a source for this piece, despite his past tweets about her work.) To date, most studies on the microintervals to have been disconcertingly small. Gibala’s initial 2005 study, published in the Journal of Applied Physiology, had just eight participants in the HIIT group. Such a tiny population tends to lead to imprecision; the margin of error widens and the means of any data set can jump around wildly. “You can discover wonderful things, none of which are true,” Ekkekakis says. That is, it’s impossible to tell from a single study whether doing a specific motion for a diminutive amount of time really does anything useful. And yet, such single studies are regularly featured in the Times and other news outlets. The seven-minute workout, meanwhile, wasn’t based on a study at all but on a 2013 “feature” story in the American College of Sports Medicine’s Health & Fitness Journal by two performance coaches at Johnson & Johnson’s Human Performance Institute in Orlando, Florida, who had developed the routine to fit in with the “hectic pace of today’s corporate world.” (Co-author Brett Klilka declined to comment, and co-author Chris Jordan could not be reached.)
Whether HIIT broadly works really depends on your definition of “work.” Researchers, mostly in Europe, have in recent years released at least five randomized control trials involving single-digit interval training. That’s the gold standard in medical science research, combining relatively large participant groups and longitudinal observation over several months or more. The findings mostly concluded that HIIT is a good but not necessarily better option than more moderate exercise in the long term. That could be seen as a point in HIIT’s favor: similar results, but significantly less time. But the research also shows that the single-minded pursuit of intensity could, paradoxically, impede people’s progress; in one trial, 80 percent of the moderate exercisers exceeded their prescribed training intensity, while 51 percent of HIIT patients fell short of theirs. That means they weren’t really doing HIIT at all. Perhaps most importantly, while getting results with short-but-intense workouts might be appealing in theory, many people work out at lower intensities or stop exercising altogether when participants’ exercise is no longer supervised by researchers. “Exercise science remains a promise. But it’s a promise that hasn’t been delivered to society yet,” Ekkekakis says. “And it hasn’t been delivered to society yet because we haven’t cracked the big problem of how to get people to stay active.”
Evidence on what exercise regimens Americans actually prefer is scant. But Casey Johnston, a health writer and author of the beginner strength training program Liftoff: Couch to Barbell, says that of all the many conversations she’s had with people about their exercise, she can’t recall a single person who’s actually tried something like the seven-minute workout, let alone stuck with it.* From what she can tell, people quickly become fatigued of the routine, and few people seem to really enjoy sweating like a dog, but that’s what all the promised benefits of HIIT demand. “Those six minutes,” as Reynolds wrote in her first entry into the short-workout genre in 2009, “if they’re to be effective, must hurt.” The success of these stories, Johnston says, is almost certainly “vicarious”—an interest among readers in what they could do, but not a lifestyle they’re adopting.
For researchers, the interest in studying HIIT might best be described as a search for the “minimum effective dose,” Maltby says. In pharmacology, the proper dose of a given drug is specific to every patient, but it must always land between the minimum effective dose and maximum tolerated dose. When it comes to exercise, the maximum most Americans seem to tolerate is minuscule—only 23 percent of adults meet the aerobic and strength guidelines, according to the CDC—so the minimum has received a lot of attention. “We’ve been interested in [the question of], how low can you go?” Gibala says. The general public seems interested too. Gibala himself is the co-author of the popular 2017 book The One-Minute Workout, which Reynolds, naturally, covered in the Times under the headline “How to Do the Shortest Workout Possible.”
These workouts are at least easier to sneak into your schedule than many other options. In reality, though, most people in the U.S. are not actually strapped for leisure time, as data from the Bureau of Labor Statistics’ annual American Time Use Survey has shown. They just don’t spend what they do have on exercise (and if that’s their choice, that is perfectly fine!). The real reasons to avoid working out are both structural and unique to the individual, making them particularly difficult to untangle. People lack confidence. Many think they need a special skill set or tailored toolkit to get moving. Plenty of would-be exercisers don’t have a safe space to be outside. And engaging with our physical selves can be emotional. “I think we underestimate the complexity of our feelings about our bodies as things we take care of—and things that we’re entitled to take care of,” Johnston told me.
Micro-HIIT training programs argue, implicitly or explicitly, that best exercise isn’t fun or interesting but optimized, and that to balance minimum effort and maximum results requires a “scientific” plan of attack and desire for quantifiable improvement. “We haven’t seen even the tiniest uptick in the number of people who, from sedentary, have become active,” Ekkekakis says. “If there’s popularity, it’s recycling the [small] percent of people in the U.S. who were active to begin with. But that’s not progress.” In many ways, these workout regimens feel like the ultimate product of the Soylent-drinking, girlboss-loving, “move fast break things” startup era from which it emerged: Rise and, as briefly as possible, grind. Yet as many of these other trends fade away, intervals seem to maintain their allure, even if few effectively put the principles into practice.
Ultimately, the latest incarnation of our centurylong HIIT obsession just goes to show that the foundational American narrative about exercise is deeply broken. “We have screwed this up from the get-go,” Ekkekakis says. The countries where people are the most physically active don’t call exercise “medicine”—in fact, they don’t call it “exercise” at all. In Scandinavia, for example, people hike and cross-country ski because it’s built into the culture and it’s fun to do. “When they come back, they’re not thinking, ‘I had a great workout,’ ” Ekkekakis says. “They’re thinking, ‘I had a great day.’ ” For what it’s worth, Reynolds, the Times writer, tends to agree. Her exercise snack reporting aside, she says she recommends her pieces, also numerous, on the benefits of a long walk.
Correction, April 19, 2022: Due to a production error, this piece originally misidentified the program Liftoff: Couch to Barbell as Litoff.
