Surprising Benefits of Brief, Intense Exercise

Robert Roy Britt
Feb 22, 2019 · 8 min read

Exercise builds the body, clears the mind and helps us live longer. We know all that. A good workout can even be enjoyable, flooding the brain with feel-good chemicals. The list goes on: improving sleep, helping battle depression, even maybe boosting general happiness.

But we humans have an unsurpassed capacity for finding excuses not to do the things that are good for us. Often we blame our perceived lack of time.

And so I wondered: How long must we exercise to actually improve health?

It’s a question that motivates researchers like Martin Gibala, a professor in the department of kinesiology at McMaster University, to do creative investigations of utterly brief exercise schemes. Or, in his most recent study, a “workout” you can do in a few minutes wherever stairs are found.

Gibala and his colleagues got some otherwise sedentary young adults to “vigorously” climb three flights of stairs, three times a day (with hours between the efforts), thrice weekly. After six weeks, compared to a control group that didn’t exercise, the stair climbers saw a 5 percent increase in cardiorespiratory fitness, as measured by peak oxygen uptake. Their legs grew 12 percent more powerful.

“This study is a reminder of the potential benefits of brief bouts of physical activity that can be done anywhere without the need for specialized equipment,” Gibala told me. Think of it as an exercise snack, he says, something to take between workouts.

The results, published Jan. 16 in the journal Applied Physiology, Nutrition, and Metabolism, add to a growing body of research showing remarkable benefits from very short-duration, high-intensity interval training that — as we’ll see below — people don’t always hate so much.

Got a Minute?

Interval training is nothing new. Runners have done it since before shoes had swooshes. A classic example: eight all-out sprints around the track with a two-minute recovery between each repetition. For an average in-shape runner, that could take 30 minutes to complete (quite a bit more for the rest of us). Who’s got time for that?

Unless you’re trying to catch Usain Bolt, you don’t need to work nearly that long to see significant health benefits. And since exercise is known to thwart depression and even promotes outright happiness, finding time for a quick workout seems more than worthwhile.

Studies going back several years have found benefits to fitness and health in high-intensity interval training (HIIT). In some of the most recent work, the amount of time necessary to yield benefits has fallen to almost unbelievably low levels.

One small study in 2018 split eight young adults into three groups, and had them do different regimes on stationary bikes:

  • Consistent intensity for 30 minutes at 50 percent of peak effort
  • Five high intensity intervals of four-minutes each, with a minute’s rest between, at 75 percent effort
  • Sprinting at maximum effort for four, 30-second intervals with 4.5 minutes rest between

The scientists measured what happened at the cellular level in thigh muscles of the participants, finding positive changes in mitochondria — the energy-creating engines in cells — known to be beneficial to health, including lowering risk for chronic disease, the researchers explained. And yes, you guessed it: “A total of only two minutes of sprint interval exercise was sufficient to elicit similar responses as 30 minutes of continuous moderate-intensity aerobic exercise,” they wrote in the American Journal of Physiology.

While the study was small and should not be construed as conclusive on its own, several others, in different labs, have generated similar results.

“The optimal number of repetitions appears to be just two.”

Shorter Intervals, Fewer Intervals

A somewhat similar study in 2014 involved three 20-second, all-out intervals on stationary bikes, sandwiched into a 10-minute session to include warmup, warm down and rests between intervals.

Folks, that’s a mere one minute of hard labor. But yes, you have to truly go all out in each 20-second session, to the point that you can’t talk.

The volunteers repeated this 10-minute workout three times a week for six weeks. The results were rather stunning. Their endurance capacity improved 12 percent, on average. They had better blood pressures and similarly good changes to their mitochondria.

And it’s possible you don’t need a ton of intervals to get most of the benefit from HIIT.

A 2017 review of 34 studies looked at VO2max (how much oxygen the body can use in a minute), before and after at least two weeks of interval training on cycles. The review found two sprints to provide the majority of benefit, with each additional sprint adding only about 5 percent more fitness improvement.

“We found improved cardiorespiratory fitness does not suffer when people complete fewer sprint repetitions,” said study leader Niels Vollaard of the University of Stirling. “The optimal number of repetitions appears to be just two.”

The findings were published in the Medicine and Science in Sports and Exercise, the journal of the American College of Sports Medicine.

Pleasure & Pain

By now you’re probably formulating a new excuse in your head: These intervals sound brutal! And they are. But not as bad as you might think.

When one group of researchers considered the emotional aspects of training, they found participants didn’t dislike HIIT training any more than traditional longer-duration aerobic work. The researchers had 30 sedentary volunteers, both men and women, do both types of exercise.

“We found that participants reported equal levels of enjoyment and preferences for HIIT in comparison to traditional exercise, despite experiencing feelings of displeasure during the higher intensity exercise,” said Matthew Stork of the University of British Columbia.

After the tests, they asked the participants to keep a journal of the exercise they did on their own for the next month. “Importantly, 79 percent of participants reported completing HIIT on their own, outside of the lab.”

To help explain what’s going on, we have to look inside the brain and the release of endorphins, naturally produced hormones known to trigger good feelings in response to everything from exercise and sex to drinking and gambling. Endorphins also act much like morphine to reduce pain.

Researchers at the University of Turku in Finland did just that in 2017, and they learned that HIIT workouts release more endorphins than traditional aerobic workouts. A veritable “endorphin rush,” said study leader Tiina Saanijoki. The findings were published in the journal Neuropsychopharmacology.

I asked Saanijoki if the endorphin rush might have something to do with why people didn’t complain so much in Stork’s greuling tests. Perhaps, she said, at least in part. But what happens in the brain during intense exercise is far from fully understood, she explained. In fact, her study, which involved super-intense intervals (as if “high intensity” weren’t enough!), yielded quite opposite effects on the test subjects’ perceptions of things like pain and stress.

“We found the release of endorphins to be associated with displeasure induced by HIIT,” she said. “On the other hand, we also found that the more pleasurable the traditional endurance training (in contrast to HIIT) felt, the more endorphins were released.”

So endorphins are linked to pleasure. And they’re linked to pain. How can both be true?

“Endorphins are the body’s painkillers, and they are released in response to many stressful situations to help people cope better,” Saanijoki explained, and they “seem to have a sort of a dual role dependent on the intensity of exercise: at moderate intensities endorphins appear to modulate positive emotionality and at high intensities it’s more related to negative emotions and protecting the body.”

Oh, and by the way, really short weightlifting workouts work, too. Several studies I wrote about previously proved this point, showing how just 13 minutes in the weight room can make as strong as someone who puts in three times the effort. And weightlifting is no lightweight when it comes to health benefits, helping with everything from physical movement and back pain to diabetes and heart health.

Many Mysteries

A lot more study is needed to figure out what’s going on in our heads when we exercise.

“For example, we don’t know if endorphin release is higher in people who are more fit (and usually report more exercise-induced pleasure than people in poor shape) or if this system develops in response to regular exercise training so that exercise-induced endorphin release would increase over time when a couch potato becomes a passionate exerciser,” Saanijoki told me.

She also pointed out that many of the studies measuring the emotional aspect of HIIT training involve people who are out of shape, and they often involve just a single session of exercise. Volunteers usually say the intense intervals feel “considerably worse than moderate exercise,” she said, but even that can depend on how demanding the HIIT protocol was. “However, if the training continues beyond one session, these emotional responses improve rapidly as the body and mind adapt to repeated training.”

In fact, in another study Saanijoki led, one group endured six sessions of super-intense interval training — these are the volunteers for science who deserve medals, folks — while another group did six sessions of moderate-intensity continuous exercise, the sort of thing you see lots of people at the gym doing on stationary bikes and treadmills.

The six sessions took place over a two-week time period.

At first, the group doing intense intervals experienced higher levels of displeasure, stress and pain, and lower levels of satisfaction. No surprise. Across the two weeks, both groups experienced less and less displeasure and pain and increased satisfaction, but the changes were more dramatic among the high-intensity group. By the sixth session, both groups felt about the same on these measures.

The findings were published last month in the the journal Medicine & Science in Sports & Exercise.

Creating Your Own Routine

None of this suggests you can skate by on minimal effort and expect to get ripped or win a marathon. Exercise is hard. I asked Gibala, the exercise snacker, if his three-times-a-week stair-climbing regime is sufficient for improving overall fitness.

“It is not meant to suggest that this is the only type of activity that people should do,” he said. “We advocate a well-rounded approach to fitness that includes activities to promote both cardiorespiratory fitness and strength.”

Gibala added that someone who’s in good shape should not see stair snacks as a replacement for their current workouts.

“But this type of activity can help with what I call ‘preventative maintenance’ or help you maintain fitness when out of your usual routine,” he said. “For example, if you are traveling and do not have access to your regular training facilities or equipment, brief vigorous stair climbing at the hotel, ideally combined with some bodyweight exercises that do not require much space or specialized equipment, can be of benefit.”

What about the total couch potato who can’t even fathom vigorously climbing anything?

“Climbing the stairs at any pace is better than nothing,” Gibala said. “So, modify the self-selected effort such that it is less than ‘vigorous.’”

Are you running out of excuses yet?


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Robert Roy Britt

Written by

Explainer of things, science & health journalist, author, former editor-in-chief of LiveScience & Space dot com, seeker of a more just and equitable world.



Interesting and useful science news and information about the human body and mind, the amazing world around us, and our place in it.

Robert Roy Britt

Written by

Explainer of things, science & health journalist, author, former editor-in-chief of LiveScience & Space dot com, seeker of a more just and equitable world.



Interesting and useful science news and information about the human body and mind, the amazing world around us, and our place in it.

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