Which has a bigger effect on the body: Exercising for longer at a moderate intensity or doing short bursts of vigorous exercise? A new study offers some insight, finding that sprinting had a much larger immediate impact on molecules than 90 minutes of moderate exercise.1
Experts say the findings, recently published in the journal Cell Reports Medicine, help explain how the body responds to different exercise intensities. But more research is needed to know if the molecular effects seen after sprinting actually translate to better health benefits, said lead author Paul Cohen, MD, PhD, an associate professor and senior attending physician at The Rockefeller University.
What Sprinting Does to the Blood
For their experiment, Cohen and his colleagues split 19 men into two groups and had them perform different exercises on a stationary bike.
The first group did sprint-interval exercises consisting of six 30-second, high-intensity bursts of cycling, with four-minute recovery periods between each round. The other group cycled continuously for 90 minutes at a moderate pace. Researchers collected blood samples from participants before and after exercises.
The team found a clear difference: the sprinting group had more substantial changes in the proteins and other molecules measured in their blood after exercise than those who cycled longer.
Sprinting also triggered an immediate uptick in proteins involved in remodeling and blood-vessel growth, while it took several hours after the longer, moderate-intensity cycling for certain proteins to show up in the bloodstream.2
Asad R. Siddiqi, DO, an assistant professor of clinical rehabilitation medicine at Weill Cornell Medical College who wasn’t involved in the research, said the results “clearly demonstrate that the body responds differently to short, intense bouts of all-out exercise versus a more prolonged and sustained bout of less intense exercise.”
That finding makes sense, Siddiqi added, given that the two types of exercise place very different demands on the body.
Still, the study had some important limitations. It was small and lacked diversity, with all participants being younger, metabolically healthy men. That means the findings may not apply to a broad population.
What Are the Implications?
Despite the caveats, the study raises an obvious question: Do bigger molecular changes actually translate to more health benefits? The study hints at that being case.
To gather insight into the longer-term health implications of the different exercises, the researchers looked at data from more than 53,000 people in the UK Biobank. They found that many of the post-sprint proteins were associated with a lower risk of chronic conditions, such as obesity and type 2 diabetes.
The molecules affected by sprinting may play “signaling roles” that could affect the overall “health benefits linked to exercise,” Cohen said.
But it’s impossible to know for sure, he added, because the study wasn’t designed to determine which type of exercise is better for health.
Moving forward, Cohen said prospective, randomized studies involving much larger groups of people will be needed. He and his colleagues are particularly curious about metabolic health.
“We are interested in studying the specific roles of some of the proteins and metabolites we identified to better understand how exercise affects whole-body metabolism,” he said.
So, What Should You Do?
The findings alone aren’t a reason to focus solely on sprinting, experts said. In reality, the difference between short high-intensity exercises and slower low- to moderate-intensity exercises “is likely on the margins,” Saddiqi said.
Instead, he said, “the most important thing is to first focus on the basics and establish your baseline of movement and fitness.”
For that, Saddiqi recommended a mix of resistance training, aerobic cardiovascular training, and balance-focused exercises. From there, “other fine tuning can occur,” he added.
When it comes to which exercises to try, he recommended finding activities you’ll actually stick with. And if you’re new to high-intensity or longer-duration exercise, it’s best to start slowly, Siddiqi said. “Shoot for a level of exertion where you feel some strain but could still maintain a conversation, and increase gradually week over week from there,” he suggested.
If you have physical or other limitations that make exercise difficult, talk to a doctor about what you can do. “Understanding a limitation is the first step to navigating it,” Siddiqi noted. “This is an area where a trusted health care or exercise professional can give guidance.”