The Science Behind the New 4-Second Workout

Woman working out in her living room.
Woman working out in her living room.
Photo: Oscar Wong/Getty Images

Researchers are racing to figure out the minimum amount of exercise needed to improve fitness and health. Findings in multiple labs have generated tantalizing headlines suggesting all you need is one lousy minute of effort or, based on one new study, a mere four seconds.

The reality is quite different.

Brief but intense workouts can absolutely improve aerobic fitness, as well as muscle strength and power. In as little as 10 to 15 minutes, you can gain fitness benefits similar to an hour of traditional, less intense exercise. And evidence suggests you can spread the effort into even shorter “exercise snacks” throughout the day.

But these workouts are never easy, nor are they as minimalist as they might sound. The vigorous routines, called high-intensity interval training (HIIT), involve warmups and cool-downs and typically require multiple intervals of strenuous effort to achieve at least 80% of your maximum heart rate, a level that causes heavy breathing and makes normal conversation difficult. And sprint interval training (SIT) workouts, which are even more intense than HIIT, elicit the sort of effort you might summon to evade a marauding velociraptor.

The simple message from all the latest research into short, high-intensity workouts: “Get out of your comfort zone sometimes,” says Martin Gibala, a professor in the Department of Kinesiology at McMaster University in Ontario, Canada, and author of The One-Minute Workout, which, for the record, takes about 10 minutes to complete.

Four seconds of hard effort, again and again and…

A new study in the journal Medicine and Science in Sports and Exercise involved an exercise regimen of multiple four-second intervals of intense effort among sedentary men and women in their fifties and sixties training three times a week for eight weeks. The workouts improved overall fitness on average, including significant increases in cardiovascular capacity (10%) and muscle power (12%).

Unlike some HIIT routines that involve just two or three intervals, these workouts required several all-out four-second sprints on a specialized stationary bike called a Power Cycle, which features a heavy flywheel. Participants typically did either 18 sprints with 30-second rests between each or 30 sprints with 15-second rest periods, explains study team member Edward Coyle, PhD, head of the Human Performance Laboratory in the University of Texas at Austin. All told, the workouts lasted 10 minutes on average.

The sprints require tremendous bursts of power. That’s important, Coyle says, because a typical person starts losing muscle fiber around age 30, and 40% of muscle can be gone by age 70. The fast-twitch muscle fibers needed for power dwindle fastest.

“Many people feel that they don’t have enough time for traditional forms of exercise. However, HIIT provides a viable, time-efficient exercise alternative that people can try.”

As with lightbulbs, the power of a given exercise is measured in watts. A beginner on a bike might average around 75 watts of output during a 30-minute ride. The power output of a typical HIIT interval might range anywhere from 180 watts during sprints lasting more than a minute to 700 watts during 20-second all-out sprints, Coyle says. But the four-second sprints recruit more than 1,000 watts of power. In turn, that level of power output combined with the relatively short rest periods generates a great aerobic session.

“Since the exercise is so powerful, your cardiovascular system is still stimulated during your rest periods,” Coyle explains in a phone interview. “You’re consuming a lot of oxygen, and you’re recovering the energy stores that you used during the sprints.”

For each participant, the first few intervals left them breathing hard, and the last few had them gasping for breath, Coyle says.

No equipment required

Coyle’s workout illustrates what’s possible with the briefest of intervals. But duplicating the effect of his specialized bike at home is impractical. That’s okay, because HIIT can be done in a variety of ways, with or without any equipment. Results can be achieved by sprinting up a hill on foot or on a bike or through a variety of other common exercises. A 2018 study by Gibala and colleagues whipped people into shape with exercise snacks, having them vigorously climb three flights of stairs three times a day but with hours between each effort.

Gibala’s latest research finds that classic calisthenics can also do the trick. His team designed an 11-minute workout session with five bodyweight-only exercises:

Each move is done for one minute at a “challenging pace,” with easy jumping jacks serving as a one-minute warmup, then a minute of walking in place after each exercise. Nine unfit but healthy men and women did the exercises three times per week for six weeks. Endurance rose by about 7% on average, and the exercisers’ legs grew stronger, compared to a control group that did not exercise, the researchers report in a January issue of the International Journal of Exercise Science.

“The latest findings are a reminder that simple, practical strategies like brief bodyweight exercises can be beneficial, without the need for specialized equipment or large time commitment,” Gibala tells Elemental. “It especially resonates in the current reality for a lot of people who are experiencing versions of lockdowns with limited access to fitness facilities and equipment.”

Try it, you might like it

Physical activity guidelines for Americans call for twice-a-week strength training, plus 150 minutes per week of moderate-intensity physical activity or 75 minutes of vigorous output — or a combination of the two. High-intensity efforts lasting less than 10 minutes now count toward that total, based on the latest revision of the guidelines in 2018.

HIIT is not a panacea, Gibala says, noting that many of the HIIT studies involve only a few participants and measure only certain markers of fitness; how these routines might translate into lifetime benefits remains to be studied. But a review of the existing research suggests they might help prevent or manage diabetes, and other experiments have found they reduce levels of bad cholesterol and improve fat metabolism and lower levels of triglycerides, which at high levels raise the risk of heart disease.

What’s more, people don’t find HIIT workouts as unpleasant as you might imagine. Coyle had wondered if the older people in his study might not be able to handle the intensity. “They did great, and they liked it,” he says.

“Just like we do with food, we can create a menu of different types of physical activity we can choose from depending on the situation and our needs. Aim for something that is realistic, attainable, and enjoyable.”

One study, which looked specifically at whether intensity begets displeasure, backs this up. Researchers had 30 people each do three different types of exercise in the lab: HIIT, the more intense SIT, and moderate-intensity continuous training more akin to traditional aerobic exercise. Enjoyment responses were similar for all three types, says study leader Matthew Stork, PhD, a researcher in exercise science at the University of British Columbia, Okanagan. Afterward, the participants were free to exercise on their own for four weeks; 79% of them chose to do at least one session of HIIT.

“Many people feel that they don’t have enough time for traditional forms of exercise,” Stork says. “However, HIIT provides a viable, time-efficient exercise alternative that people can try.”

It’s also important to note that intensity is a relative thing. What would exhaust one person might be easy for someone who’s in shape. Pushing yourself physically is how you gain fitness, but it should be done sensibly, both for safety’s sake and to avoid burnout.

“I personally don’t love the idea of ‘push yourself to the limit’ as something we should be promoting across the board, particularly with individuals who are low active and less experienced with exercise,” Stork says. “For less experienced individuals, pushing too hard too soon has the potential to deter them from continued engagement.”

We humans did not evolve to exercise — working out without the dangling carrots of procreation or survival just isn’t in our nature.

If you struggle to get excited about jogging, aerobics, or other extended workouts, consider some natural activities like a brisk walk, dancing, or gardening, and maybe challenge yourself to a few pushups and maybe even a little HIIT — all proven ways to improve fitness. And it’s never too late to accrue benefits, studies show.

“Just like we do with food, we can create a menu of different types of physical activity we can choose from depending on the situation and our needs,” Stork says. “Aim for something that is realistic, attainable, and enjoyable. That could be a long hike or a short HIIT session—whatever works for you based on your needs and physical capabilities. Every little bit counts.”

Explainer of things, independent health and science journalist, author, former editor-in-chief of LiveScience and Space dot com.

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