What’s the point of a 5-minute workout, really?

A lucky few find a fitness routine they love and stick with it. But many of us just want to finish our workout as quickly as possible. For those in the latter camp, it’s hard to resist headlines that claim we can get in shape in five minutes or less a day.

That kind of thing seems too good to be true, but emerging research suggests these micro-workouts — a few 20-second rounds of stair-climbing, four-second sprints on an exercise bike, or a two-minute rush to catch a bus — can improve fitness, prevent disease and prolong a person’s life.

These activities are easier to fit into your schedule than the recommended 150 minutes of moderate exercise per week (or 75 if you make it vigorous by jogging, for example). But some scientists say such micro-workouts, also called exercise snacks, are oversold. And even those who tout their benefits say claims that they’re as good as or better than more traditional workouts are going too far.

The concept is based on more than two decades of research into HIIT, or high-intensity interval training. HIIT involves a series of near-full efforts, usually lasting 20 to 60 seconds, interspersed with short rests and then repeated over and over. Some studies show that HIIT workouts provide many of the same benefits as regular, moderate-intensity exercise—including improved aerobic fitness and blood vessel function—in less time.

So the researchers wondered if just a few hard intervals spread throughout the day would be just as effective. Can short bursts of activity still have benefits with hours of rest in between instead of seconds?

So far, small lab studies show that micro-workouts can move the needle on some measures of health. In one typical example, 12 otherwise non-exercising young adults ran up three flights of stairs (60 steps) three times a day, three days a week. After six weeks, their aerobic fitness, as measured by oxygen uptake, had improved by five percent. That’s about what you’d expect from three days of brisk walking for 30 minutes each week, said Jonathan Little, lead author of the study and a professor at the University of British Columbia.

Another study of more than 25,000 British adults found that just one to two minutes of vigorous movement three times a day was associated with an estimated 40 percent lower risk of death and about a 50 percent lower risk of death from cardiovascular disease compared to people who did no vigorous activity.

But observational studies like this can’t prove cause and effect. And that benefit is less robust than you might expect for those who meet government exercise guidelines. Still, if done regularly and safely, such short bursts may be a meaningful start for otherwise sedentary people, said Emmanuel Stamatakis, a professor at the University of Sydney and lead author of the study.

Exercise makes us fitter and healthier by stressing our muscles and cardiovascular system, which then become stronger and more efficient, said Philip Skiba, M.D., an exercise physiologist and physician in Park Ridge, Illinois. . Minute for minute, intense efforts stimulate muscles more than moderate workouts — but bursts of less than 20 seconds are unlikely to produce major health improvements, he said.

In fact, even the benefits of HIIT can be overstated, said Panteleimon Ekekakis, a professor of exercise psychology at Michigan State University. Most laboratory studies of brief but intense efforts are small, which limits their statistical power. Outside the lab, wrist-worn activity monitors allow studies of larger groups of people, but may not accurately capture factors such as intensity, especially over short periods.

Plus, while studies show that intense intervals are safe, even for people in cardiac rehabilitation, vigorous exercise can in some cases increase the risk of sudden heart problems. So it’s wise to check with your doctor first if you have a history of heart problems or have been sedentary for years, Dr. Skiba said.

Finally, micro-workouts may not actually motivate people to exercise, Dr. Ekekakis said; research shows that time constraints are not actually the biggest barrier. More importantly, he said, a lot of people don’t like it, especially when they’re starting out. And intense workouts are often more unpleasant than moderate ones.

Intense bursts of effort for five minutes or less one or more times a day probably provide some benefit, especially if you really don’t have any other time to exercise or if you spend long stretches glued to your chair.

More research, now underway, will determine the optimal “dose” — how many bursts you need and how long and severe they need to be to cause meaningful changes in your health, Dr. Little said.

However, decades of studies with many thousands of participants more clearly confirm the health benefits of getting about 150 minutes of moderate activity or 75 minutes of vigorous movement per week. So what you shouldn’t do is replace another type of exercise habit—especially one you enjoy—with micro-workouts.

“That would be a real risk based on what we know right now,” Dr. Skiba said.

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