Exercise stimulates the brain due to its effect on muscles

Exercise plays an important role in brain health by causing the muscles to release molecules associated with cognitive function, a recent study found.

Research published in the Proceedings of the National Academy of Sciences shows that when nerves that stimulate muscles are activated, they also send signals to the brain, releasing bioactive molecules and nanoparticles that improve brain function.

The results highlight the importance of maintaining musculoskeletal health not only for cardiovascular health or mobility, but also to counteract neurodegeneration, said Hongrong Kong, Ph.D., professor in the department of chemical and biomolecular engineering at the University of Illinois at Urbana-Champaign and co-author of the study..

He explained that: “Maintaining neuronal innervation is critical to allowing muscles to produce biological factors that benefit the brain. With regular muscle contractions, the muscles not only release these beneficial factors, but also help maintain the innervation necessary for the nerves to continue sending signals to the muscles. These signals are necessary to regulate the release of neurotrophic factors into the brain."

The study stimulated muscles with glutamate to see how nerve function responded. The researchers used models of muscle tissue, one innervated and one uninnervated, and found that innervated tissue sent more signals to the brain.

Because some of the function of neurons in muscle can decline with age or injury, researchers were interested in how this loss would affect brain health.

How does exercise affect brain function?

In this study, researchers did not observe people exercising. Instead, they studied muscle tissue models, which means it was not possible to draw direct conclusions about specific forms of exercise and their effects on brain health.

Kong said previous research on exercise and brain health has shown a direct correlation between the size of the hippocampus and regular physical activity. But for this new study, researchers looked at nervous system and musculoskeletal function to better understand the interactions between the brain and body.

“Our study did not prove how exercise can directly improve cognitive function,” Kong cautioned. “Several studies have already shown that regular exercise can improve cognitive function in adults. In these studies, participants were asked to exercise regularly and changes in the size of their hippocampus were monitored."

"The results show that people who regularly do aerobic exercise have larger hippocampi and perform better on spatial memory tests. We focused on how neurons associated with muscles influence one of the pathways between muscles and the brain." — Hyunjun Kong, PhD

Ryan Glatt, CPT, NBC-HWC, a senior brain health coach and director of the FitBrain program at the Neuroscience Institute in Santa Monica, California, who was not involved in the study, said it will take time to fully understand the effects of exercise on the brain, and future studies in humans will need to take that into account.

“The length of time needed to observe the effects of exercise on cognitive function can vary depending on the type, intensity, and frequency of exercise, as well as individual differences in age, baseline cognitive function, and health status,” Glatt said.

“Studies typically show observable effects over a period of weeks to months. It’s important that future studies account for these variables to accurately assess the time frame,” he noted.

What Types of Exercise Are Best for Brain Health?

Regular exercise has measurable benefits for brain health. For example, boxing has been used to help people with Parkinson's disease.

Glatt noted that some types of exercise may be more effective than others at improving brain health, particularly those that require cognitive function.

"Aerobic exercise such as running, swimming and cycling, which improve cardiovascular health, are widely known for their positive effects on brain function," he said.

"However, activities that combine physical and cognitive activity — such as dance and team sports — may offer additional benefits due to the need for coordination, rhythm and executive function," he added.

Can exercise reverse or slow cognitive decline?

Kong suggested that physical activity could potentially reverse or slow the cognitive decline associated with aging.

"As people age, they gradually lose well-formed neuromuscular junctions between nerves and muscles, which impairs the ability of muscles to be regulated by nerve signals and, accordingly, reduces their ability to secrete factors critical to brain function," Kong explained.

"With appropriate training or stimulation of muscle contractions, muscles can produce factors that help maintain these neuromuscular junctions, preventing denervation. As a result, older adults can still have functionally innervated muscles capable of producing important factors that improve cognitive function in the brain," he noted.

Glatt indicated that a sedentary lifestyle with relatively low levels of physical activity may be associated with a higher risk of cognitive decline.

However, he cautioned that there are various individual differences relating to genetics, lifestyle and environmental factors.

"Exercise is increasingly recognized as a supportive intervention for people with weakened cognitive function, including those suffering from age-related declines or conditions such as Alzheimer's disease. Physical activity can improve blood flow to the brain, reduce inflammation and stimulate the release of growth factors, which may help maintain or improve cognitive function," Glatt said.

"Although exercise is beneficial for maintaining cognitive health and potentially slowing the progression of decline, evidence for its ability to reverse existing cognitive decline is still inconclusive. Most studies suggest that exercise may promote a slower rate of decline and better overall brain health, but the opposite may be true for Addressing established cognitive deficits requires more extensive research," he cautioned.