Sprint intervals changed 714 blood proteins in 19 young men, against 7 after a 90-minute ride

Three minutes of all-out effort beats an hour and a half of steady exercise: that was how one study was widely reported this summer. The experiment behind it took blood from 19 young men before and after they cycled, and what it measured was the chemistry of that blood, not how healthy anyone became.

The work comes from Paul Cohen’s laboratory at Rockefeller University in New York and was published in Cell Reports Medicine in August. Six 30-second sprints left the bloodstream carrying a very different set of proteins. Ninety minutes of moderate cycling barely moved them. The gap is large, and what it means for health is a separate question.

What did the sprints do that the long ride did not?

Luke Olsen, the postdoctoral fellow who ran the study, started with blood stored from an Australian training trial. Of the original 28 participants recruited, 19 were used for this study, all of them healthy men with an average age of 26. One group had done six all-out 30-second sprints on a bike, interspersed by 4-min recovery periods. The other had ridden continuously at a fixed power for 90 minutes. Blood was drawn before, immediately afterward and three hours later.

The team then counted. Their protein test detected and quantified 2,884 proteins across all participants and time points. After the sprints, nearly a quarter (714 proteins) of the total detected proteins had changed, almost all of them upward. After the long ride, only 7 proteins were differentially regulated, a number that crept up to 19 three hours later. Metabolites, the small molecules left behind as cells burn fuel, told the same story at a different pace. The sprints changed 203 of them at once, while the steady ride changed 31 at first and 183 three hours on.

Fitness did not erase the gap. A subset of the men trained for eight weeks and repeated the test, and the same split appeared. “What’s exciting here is that just a few minutes of intense exercise can trigger a significant molecular response,” Cohen said in a statement from the university. “And we still see it after eight weeks of training, which tells us this response isn’t simply a product of the body struggling to keep up with unfamiliar stress.”

To see whether the altered blood did anything, the researchers bathed human fat cells in it. Plasma taken after sprints switched activity up or down in more than 1,600 genes. Plasma taken after the moderate ride changed 25.

What are exerkines, and why count blood proteins after exercise?

Muscles, liver and fat release chemical messages when the body works hard, and those messages travel in the blood to other organs. Researchers call them exerkines. A 2022 review in Nature Reviews Endocrinology defines them as signals released in response to acute and/or chronic exercise, with a list that has multiplied since the first was found in 2000. It says that exerkines have potential roles in improving cardiovascular, metabolic, immune and neurological health. The same review is frank that the molecular mechanisms that underlie the beneficial effects of exercise remain poorly understood.

Counting those messages is a way into that gap. An independent group at Stanford did something similar in 2020, profiling the blood of 36 well-characterized volunteers, before and after a controlled bout of exercise to exhaustion. Their analysis revealed thousands of molecular changes touching energy use, inflammation and tissue repair. The Rockefeller study agrees with that picture and adds a comparison the earlier work lacked: the same measurements at two very different intensities. A separate study this year took the cell-by-cell route, examining exercise and the immune system in people who train regularly.

Do the sprint proteins mean better health?

Here the study leans on other people’s data. The UK Biobank holds protein measurements and medical records for 53,026 human participants. Olsen and colleagues looked up their exercise-responsive proteins there and picked out 33 whose higher levels went with less obesity, type 2 diabetes and related metabolic disease. Nearly all of these proteins (32 of 33) were found to be differentially regulated by sprinting. The moderate ride moved three.

A detail in the paper matters for how much weight that can bear. Across all the proteins that exercise changed, most disease links pointed the other way, toward higher risk. The authors call that consistent with prior literature showing that acute exercise induces a transient inflammatory and stress-response program, and they chose to focus on the protective minority. The 33 are a selected list.

Other kinds of evidence do point the same direction as the headline. A Nature Medicine study followed more than 25,000 people in the UK Biobank who did no formal exercise and wore activity trackers. Those who managed a few one-to-two-minute bursts of hard movement a day died at lower rates over about seven years, and the authors concluded that small amounts of vigorous nonexercise physical activity are associated with substantially lower mortality. Training studies show a modest edge as well. A meta-analysis in Sports Medicine of 28 trials compared high-intensity interval training (HIT) with endurance training. It found gains in VO2max, the standard laboratory measure of aerobic fitness, being greater following HIT when compared with endurance training. Both lines of research involve repeated exercise over weeks or years, which a single blood test after one session cannot stand in for.

A small, mostly male sprint study with one tangle in its design

The authors name the first weakness themselves: the most notable limitation, they write, is the small and male-biased cohorts. Nineteen men supplied the main result and thirteen of them the training comparison. The two extra groups added only six women.

The comparison also bundles two things together. The sprint session was hard and short, the steady session easy and long, so a difference between them could come from intensity, from duration or from both. The paper says so directly: the exercise paradigm could not separate these two variables. And because the test counted proteins without tracing them, the team was unable to determine organ-of-origin or destination for many of the signals.

What the study did not include is any measure of health. Nobody’s blood pressure, blood sugar or fitness was compared between sprinters and steady riders as an outcome of the protein changes, and the disease links come from a separate population measured at rest.

That leaves a clear and limited result. Hard efforts send a much larger wave of signals through the blood than gentle ones, and the wave survives getting fitter. Olsen’s own summary is careful: exerkines “are highly sensitive to exercise intensity and may be the key mediators of the health-promoting effects of short bursts of vigorous exercise.” The word doing the work there is “may.” Current World Health Organization guidance counts both kinds of exercise and holds that some physical activity is better than none.

Whether a bigger wave of blood signals makes sprinters any healthier has not been tested.