Three minutes of intense exercise may have more beneficial impacts on our physiology and health than 90 minutes of more moderate exertion.
That idea could sound far-fetched. But in a groundbreaking new study published in August in Cell Reports Medicine, scientists found that the blood of people who completed three minutes’ worth of all-out exercise — in 30-second bursts over the course of 23 minutes — teemed afterward with far more molecules associated with health improvements than the blood of people who rode bikes relatively moderately for an hour and a half.
Those molecules may then travel through the blood from one organ to another carrying messages from the muscles, liver, immune cells, intestines or other organs to far-flung tissues such as the brain, body fat or adrenal glands. These messages can spark reactions that may influence and improve health, the scientists found.
After several minutes of brief, intense exercise, there were signs of greater interorgan cross talk than after longer, gentler workouts.
With these results, the ambitious new study helps both to answer and raise new questions about how exercise works and which types may be most potent.
“We know exercise is associated with beneficial health outcomes,” said Paul Cohen, a cardiologist and associate professor of molecular metabolism at The Rockefeller University in New York City, who oversaw the new study. “But we don’t have a deep understanding of how that occurs and how different organs signal to one another during and after exercise.”
The new study suggests that almost any exercise meaningfully changes us at a microscopic level. But it’s possible that, as the researchers write, “not all exercise is equal.”
Intense exercise is linked to longevity
Intensity may be one of the toughest aspects of exercise to grasp (or enjoy). Most of us understand duration and frequency; the first is how long you exercise, the second how often. But intensity is a more subjective measure of how hard the exercise feels to you. Your intense workout may be different from your partner’s or your neighbor’s or your best friend’s.
Intense exercise should feel to you like an 8 out of 10 in terms of difficulty. Moderate exercise, by comparison, should be around a five.
A growing body of research suggests intense exercise might be more beneficial. In particular, a large-scale 2024 study of about 7,500 middle-aged men and women found that those who almost never completed any intense physical activities were nearly 40 percent more likely to die prematurely than people whose activities were even a little more strenuous.
But that study and others haven’t been able to tell us why intense exercise might be uniquely good for us.
3 minutes vs. 90 minutes
So, for the new study, the researchers had 19 healthy young men visit a lab and either ride a stationary bicycle at a relatively moderate pace for 90 minutes or do all-out sprint intervals. These consisted of six 30-second bursts of pedaling at the highest pace the men could manage, interspersed with four minutes of rest between. By the end, they’d finished three minutes of actual, intense exercise (during a 23-minute session).
The researchers drew blood three times: before the workout, immediately after and three hours after. Then they ran the blood through a high-tech system to categorize and count every protein.
The before-and-after blood signatures proved to be quite different, especially if the men had done intervals. More than 700 proteins in their blood showed greater or lesser abundance immediately after their short, hard workout.
On the other hand, only seven proteins had changed in the blood of the men who’d ridden moderately for 90 minutes, at least right away. After three hours, an additional 12 looked different.
The effects of intense exercise linger
The brief intervals’ effects had utterly swamped those of the moderate riding. But were those changes beneficial and due to the exercise, or were they signaling severe stress from sudden, unfamiliar exertion? In that case, the effects wouldn’t be beneficial. They also were unlikely to linger if the men grew accustomed to those workouts.
For clarity, Cohen and his colleagues, which included postdoctoral researcher Luke Olsen, the study’s lead author, had some volunteers continue their assigned exercise routine a few times a week for eight weeks. All grew fitter, their bodies adjusting to the new workouts.
The scientists repeated the blood draws.
And the results remained broadly the same. Blood from the men who’d practiced intense exercise for about 72 minutes in total over the two months showed immediate changes in hundreds of proteins, compared with fewer than 10 from the men who’d ridden moderately for at least 216 hours.
The impacts of that first hard workout hadn’t been a fluke, the scientists reasoned. They’d been the start of exercise responses that would last.
How organs talk to each other during exercise
Big questions still remained, including which organs were pumping out the proteins during exercise and which were receiving them, information with health implications.
Using data from previous research about gene activity patterns tied to specific organs, Cohen and his colleagues looked for those patterns in proteins altered after intense or moderate exercise to trace them to their origins, which included not only muscles, but also immune cells, fat tissue, the liver, pancreas, pituitary gland, intestines, brain and others.
Most of these tissues, in turn, absorbed proteins from elsewhere — receiving, in effect, microscopic notes from other organs about how to respond to exercise.
And the tissues did respond, according to another arm of the study. When the scientists added plasma from the men who’d completed interval or moderate training to isolated human fat cells in dishes, they saw far more changes to the cell’s gene expression afterward if the plasma had come from the men who’d sprinted all out for a few minutes than from those who’d cycled moderately.
The effects of intensity on long-term health
One overarching issue still needed to be addressed. “We realized that people in the public would want to know, ‘What does this mean for me?’” Cohen said.
So, the scientists turned to existing data from about 50,000 adults in Britain. The data included typical blood protein levels and their long-term health. In effect, their protein signatures already had been linked to risks for a variety of chronic diseases.
Cohen and his colleagues checked the proteins that had changed most after either intense or moderate exercise against those in the database and found 32 from the sprinters were closely linked to reduced risks for later diseases, including heart disease, obesity and Type 2 diabetes. Only three proteins altered after moderate cycling were associated with better long-term health.
How to add intensity to your activities
This doesn’t mean you should stop all prolonged, mellow workouts in favor of brief, intense interval sessions, Cohen said. “All we can say at this point is that in this study, among subjects who were exclusively young and healthy and male, these are the associations we saw.”
The study doesn’t say whether women, older people or anyone with existing health problems would see comparable results. It also doesn’t tell us if three minutes of draining, all-out exercise is the ideal dose of exertion. Would two minutes prompt similar changes? What about 10 or 15 minutes of slightly less strenuous but still challenging exercise, such as jogging up hills?
Finally, the results don’t explain why a few minutes of hard exercise prompts a greater physiological response than other exercise, though Cohen and his colleagues suspect the answers involve, in part, the unique demands it makes on cells’ energy reserves.
More study is, of course, needed. “I think this work provides impetus and direction for future research,” said Martin Gibala, a professor of kinesiology at McMaster University in Ontario, Canada, who’s long researched the effects of exercise intensity but wasn’t involved with the new study.
Even in advance of that science, though, we can take the study’s findings to heart and pick up the pace of our movements, at least sometimes. (Check with your physician if you have existing medical concerns.) Run up the stairs instead of strolling. Choose a tree or other landmark ahead of you during your next outdoor workout and hurry toward it, slowing as you arrive. Then look for another landmark ahead to rush toward.
But if even that much intensity seems daunting, keep moving however you can, Cohen said. “I’m a cardiologist, and I’m always counseling my patients to be active. I don’t think any of them are as active as the subjects in this study. But we encourage everyone to as active as they can be,” whether that’s for 90 minutes at a time, or three.
Do you have a fitness question? Email [email protected] and we may answer your question in a future column.
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