Just a few minutes of very hard exercise may trigger surprisingly large changes throughout the body.
New research from Rockefeller University found that short bursts of all-out sprinting changed hundreds of substances circulating in the blood almost immediately.
The response was much larger than researchers saw after far longer sessions of moderate exercise.
Six 30-second sprints, adding up to only three minutes of sprinting, changed nearly one-quarter of the blood proteins the scientists measured.
By comparison, 90 minutes of steady, moderate cycling changed fewer than one-quarter of 1% of the measured proteins immediately after exercise. Moderate treadmill running produced more changes than cycling, but still far fewer than sprinting.
The findings were published in the journal Cell Reports Medicine. The research was conducted by Rockefeller scientists including postdoctoral fellow Luke Olsen and colleagues working with senior researcher Paul Cohen.
Exercise affects much more than muscles. When the body moves, organs and tissues release chemical signals into the bloodstream that can communicate with other parts of the body.
Scientists sometimes call these exercise-related signals “exerkines.” They include proteins and small molecules that may help explain why physical activity can improve heart health, blood sugar control, metabolism and many other aspects of health.
The Rockefeller team wanted to know whether the intensity of exercise changes this chemical conversation. Instead of simply measuring heart rate or calories burned, they examined large numbers of proteins and metabolites in blood before and after different types of exercise.
Sprinting produced the most dramatic immediate response. In addition to altering many proteins, it changed more than 200 metabolites, which are small molecules created or used during the body’s normal chemical processes.
Many of the proteins that rose after sprinting were involved in blood vessel growth, tissue repair and communication between hormones and cells. These rapid changes suggested that the body was sending a powerful whole-body signal in response to the brief but intense effort.
Researchers also uncovered an unusual way some proteins entered the bloodstream. Rather than waiting for cells to manufacture new proteins, the body appeared to release pieces of proteins that were already attached to cell surfaces.
This fast process is called ectodomain shedding. In simple terms, enzymes cut off the outside portion of certain surface proteins, allowing those pieces to enter the blood within a very short time.
The researchers then asked whether blood collected after exercise could directly change the behavior of other cells. They exposed human fat cells in the laboratory to blood taken from participants after sprinting.
The fat cells showed widespread changes in gene activity. Genes involved in fuel use, hormone responses and the ability to sense nutrients became more or less active, suggesting that sprint-related blood signals can influence how fat tissue behaves.
Blood collected after moderate cycling produced a much smaller immediate response in the fat cells. This does not mean moderate exercise was biologically inactive, because its effects appeared to follow a different timetable.
About three hours after moderate endurance exercise, researchers saw a meaningful rise in fatty acids and proteins released by the liver. These slower changes are consistent with the body’s need to supply fuel during and after prolonged exercise.
The scientists also investigated whether the proteins affected by exercise were related to long-term health. They compared their findings with health information from more than 53,000 participants in the UK Biobank.
Many exercise-responsive proteins were associated with lower rates of cardiovascular and metabolic disease. The pattern was especially strong for obesity, type 2 diabetes and other disorders involving metabolism.
Of 33 proteins linked with lower disease risk, 32 were changed by sprinting. Only three were altered by moderate exercise in the same immediate period, and more than one-quarter of the 33 proteins were also associated with slower biological aging.
The researchers found that the strong sprint response was still present after participants had completed eight weeks of training. That suggests the effect was not simply caused by untrained bodies reacting badly to an unfamiliar physical challenge.
The study provides an intriguing explanation for why short, intense exercise can produce health benefits. Intensity may trigger a distinctive chemical message that travels through the bloodstream and tells distant tissues to change their behavior.
However, the results do not prove that three minutes of sprinting is healthier than 90 minutes of moderate exercise. The two forms of activity produced different responses, and moderate endurance exercise has extensive evidence supporting benefits for the heart, brain, fitness and longevity.
The study also focused heavily on short-term molecular changes rather than long-term disease outcomes. Finding that a protein is associated with lower disease risk does not prove that exercise changes that protein enough to prevent disease.
Very intense sprinting is also not suitable for everyone, particularly people with certain heart conditions, injuries or low fitness levels. Exercise programs should match a person’s health and ability, and vigorous training may need to be introduced gradually.
The most useful conclusion is that exercise intensity appears to matter at the molecular level. Sprinting and endurance activity may improve health through partly different pathways, and understanding those pathways could eventually help scientists design better exercise programs or even discover new treatments inspired by the body’s response to movement.
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