Working Out Harder Could Keep the Brain Sharper

Lisa Jhung

December 21, 2022

Need to motivate patients to power through tough workouts? Try telling them this: Those few moments of extra effort may help the brain stay sharp for years to come.

Although exercise has been associated before with improved brain function, a new University of Michigan study suggests individuals can bolster these benefits simply by pushing harder.

The study adds to growing evidence that exercise intensity matters just as much as amount. A recent UK study found that putting more effort into workouts could help lower heart disease risk and add years to one's life. Even short bursts of activity seem to help as long as you work a bit harder.   

Scientists are still figuring out how exercise helps the brain, but some experts believe it has to do with the release of brain-protective molecules like cathepsin B (CTSB) and brain-derived neurotrophic factor (BDNF). 

"These two molecules have been shown to be potentially protective of cognitive health," says study author Corey Mazo, a PhD student and researcher in the university's Human Bioenergetics Laboratory. "Intensive bouts of exercise were the most effective at increasing circulating levels of CTSB and BDNF." 

In the study, published in Brain Plasticity, 16 healthy young adults ran on treadmills at varying intensities — 40%, 65%, 80%, and 100% of their VO2 max, the amount of oxygen the body uses when an individual exercises as hard as they can. (Going at 100% of VO2 max feels like going all-out — a person would be breathing hard and unable to sustain the effort for very long.)  

Blood samples taken before and 30 minutes after the 80% and 100% VO2 max workouts revealed a 20% and 30% increase in CTSB levels, respectively. Samples taken after the 40% and 65% workouts revealed no increase. The authors also found a modest trend for increased BDNF following intense exercise. 

The study sheds light on how these rises might happen. Muscle biopsies taken before and after the high-intensity (80%) workout showed presence of CTSB and BDNF. They also revealed an increase in BDNF gene expression, which sets the stage for making BDNF. This suggests that muscle contractions (the lengthening and shortening of muscles when you move) may play a role in triggering the brain-boosting benefits. 

The study builds on previous research linking exercise with brain benefits, the researchers say. Physically active adults have a nearly 40% lower risk of cognitive decline than their more sedentary counterparts. And in a 2020 study review, participants who exercised the least were more than twice as likely to develop Alzheimer's as those who exercised the most.  

"Next to brain-supporting nutrition, nothing is as critical to preserving brain volume, memory, and general cognitive function as regular vigorous exercise," says Joseph Keon, author of The Alzheimer's Revolution, who was not involved in the study. "Exercise literally changes the size, structure, and function of the brain."

The study doesn't tease out how intense exercise would affect older adults already experiencing a decline in brain function. And the small sample size means more research will be needed to confirm the results and also to determine the exact dose of intense exercise — like how long and how often — required to ward off cognitive decline in different populations, Mazo says. 

For now, patients should consider adding bouts of intense exercise to their fitness routine, if they don't already. However, they should first talk to a clinician if they are new to exercise or have a medical condition.


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