A recent study published in the journal Neuron suggests that the brain plays a direct role in how the body builds endurance after physical activity. Scientists found that a specific group of brain cells springs into action immediately after a workout, sending signals that tell the muscles to adapt and grow stronger. This research provides evidence that the benefits of exercise depend on the brain as much as they depend on the muscles themselves.
The study was led by J. Nicholas Betley, a professor of biology and neuroscience at the University of Pennsylvania, Erik Bloss, an assistant professor at The Jackson Laboratory, and Kevin W. Williams, an associate professor of internal medicine at UT Southwestern Medical Center. The project’s co-first authors were Morgan Kindel, a neuroscience doctoral candidate at the University of Pennsylvania, and Ryan J. Post, an assistant professor at Providence College.
The scientists conducted the research to explore how physical training creates long-lasting health benefits. People naturally assume that building endurance is a process that happens entirely within the body. When a person runs or lifts weights, the heart pumps harder and the muscles do the heavy lifting. As a result, changes in the cardiovascular system and muscle tissues seem to be the obvious source of increased stamina.
However, the scientists suspected that the central nervous system might do more than just react to physical stress. They designed this project to see if the brain actively coordinates the body’s metabolic response to physical activity. “Our labs have long been interested in how the brain regulates metabolism, and exercise is one of the most powerful metabolic and health interventions,” Williams told PsyPost.
At UT Southwestern, Williams runs a laboratory that examines how neural networks control feeding behavior, energy expenditure, and glucose metabolism. “We previously published that hypothalamic neurons undergo structural and functional changes in response to exercise,” Williams said. “In this study we addressed how hypothalamic neurons drive the peripheral adaptations to exercise.”
Specifically, the researchers wanted to understand the function of a cluster of cells in the ventromedial hypothalamus. The hypothalamus is a small region deep in the brain that helps regulate metabolism, energy levels, and hunger. The authors focused on cells known as steroidogenic factor-1 neurons within this brain region.
“Steroidogenic factor-1 neurons in the ventromedial hypothalamus are well positioned to integrate signals about energy status and physical activity, so we set out to test whether they play a causal role in exercise-induced endurance improvements,” Williams said.
The researchers designed a series of experiments using adult male and female mice to track and alter the activity of these neurons. To test the role of these specific brain cells, the scientists genetically modified a group of mice so that their steroidogenic factor-1 neurons could not communicate. They achieved this by introducing a tetanus toxin into these specific neurons, which prevents them from releasing chemical signals.
The researchers then placed these mice on a motorized treadmill for an exercise stress test. They gradually increased the speed until the animals reached physical exhaustion. While the modified mice consumed oxygen at normal rates, they exhausted much faster than normal mice. They also burned through their energy reserves differently, showing an altered balance of carbohydrate and fat utilization.
The researchers collected skeletal muscle tissue from the mice three hours after a final treadmill session. They analyzed the tissue using a laboratory technique that lets scientists see which genes are turned on or off. In normal mice, exercise triggered a cascade of genetic changes in the muscles that improve energy use.
In the mice with silenced brain cells, these normal genetic changes in the muscle were almost entirely absent. The lack of brain signaling stopped the muscles from remodeling themselves. This finding suggests that the muscles need a permission signal from the brain to grow stronger.
Next, the researchers put the mice through a three-week training program. The mice ran on the treadmill five days a week at gradually increasing speeds. Normal mice rapidly improved their running times and distances over the three weeks. Mice with the silenced brain cells failed to improve their stamina at all.
“We were struck by how pronounced the effect was when these neurons were silenced,” Williams said. “Disrupting SF1 neuron activity significantly blunted endurance improvements even when the animals were still running, which suggested the neurons aren’t just responding to exercise, but are actively mediating adaptation. That degree of specificity was compelling.”
Even when given free access to a running wheel in their cages, the modified mice showed almost no interest in running. To ensure this was not just a side effect of poor initial fitness, the scientists ran another test. They knocked down a different activity-related gene in the mice, which caused the animals to gain weight and run poorly at first. Despite their poor initial fitness, these mice still rapidly gained stamina after just a week of training, showing that the tetanus toxin modification was uniquely blocking endurance gains.
To understand what these brain cells were doing in real time, the scientists used miniature microscopes mounted on the heads of the mice. These microscopes recorded calcium activity inside the neurons, which is a reliable marker of when a brain cell is firing. During a single running session, the researchers noticed that a specific subset of these neurons became highly active. Interestingly, these cells did not peak in activity during the run, but immediately after the exercise ended.
As the mice continued their three-week training regimen, the researchers tracked these same individual cells. They found that repeated exercise increased the total number of brain cells that activated after a run. The magnitude of the electrical activity in these cells also grew stronger as the mice became more fit. This provides evidence that the brain learns to respond more robustly to physical training over time.
Using a technique to measure electrical currents in individual brain cells from slices of brain tissue, the scientists observed that the resting electrical charge of these cells shifted in the exercised mice. The spontaneous firing rate of the neurons more than doubled in the mice that exercised compared to sedentary mice. There were also no completely silent neurons in the exercised group, unlike in the sedentary group.
The scientists also looked closely at the physical structure of these neurons. Brain cells connect and communicate at junctions called synapses, which often sit on tiny branch-like structures known as dendritic spines. By counting these microscopic structures, the authors found that the exercised mice had twice as many dendritic spines as the sedentary mice. This physical change provides evidence that repeated exercise physically rewires the brain to receive more signals.
Finally, the researchers used a technique to manipulate these brain cells with light. By shining a specific wavelength of light through a tiny fiber optic cable into the brain, they could turn the neurons on or off like a switch. During a three-week training program, the researchers turned off the brain cells for fifteen minutes immediately following each daily run. Because of this brief manipulation, these mice failed to improve their stamina.
In a separate group of mice, the researchers used the light to stimulate the neurons for a full hour after each training session. The mice receiving this post-workout brain boost gained significantly more stamina than mice undergoing the exact same physical training. They could run longer and at higher speeds by the end of the trial. This suggests that the activity of these brain cells after a workout is an essential trigger for building physical endurance.
While these findings offer a new way to think about exercise, readers might misinterpret the brain’s exact role. This study does not imply that muscle tissue is unimportant or that a person can simply think their way to better fitness. Physical movement is still required to start the biological process.
“The brain isn’t just a passenger during exercise,” Williams said. “It is actively involved in the adaptations that make you fitter over time. We found that a specific population of hypothalamic neurons is required for the endurance gains that come with regular aerobic training.”
The study has some limitations that require consideration when interpreting the data. “This work was performed in preclinical models, specifically in mice,” Williams said. “While the hypothalamic circuits we study are conserved across mammals, translating these findings to humans requires caution.”
“We also focused on endurance performance as our primary outcome,” Williams added. “It will be important in future work to examine how broadly these neurons influence other aspects of exercise adaptation, such as metabolic flexibility or cardiovascular responses.”
Future research will try to identify the exact biological pathways that connect the tired muscles to this specific brain region. “We want to better understand the circuitry involved in this response,” Williams told PsyPost. “Which signals do SF1 neurons receive/send, and to where, to drive these adaptations?”
Understanding these pathways tends to open the door for new medical treatments. “This raises the possibility that targeting these brain circuits could one day help people who are unable to exercise fully benefit from some of its metabolic effects,” Williams said. “Longer term, understanding these pathways at a mechanistic level may open new therapeutic strategies for metabolic disease.”
“Exercise remains one of the best medicines we have, and understanding its biology in the brain is still in its early days,” Williams said. “Studies like this remind us that the brain’s role in physical fitness is far more active and specific than we once appreciated.”
The study, “Exercise-induced activation of ventromedial hypothalamic steroidogenic factor-1 neurons mediates improvements in endurance,” was authored by Morgan Kindel, Ryan J. Post, Kyle Grose, Louise Lantier, Eunsang Hwang, Jamie R.E. Carty, Lenka Dohnalová, Lauren Lepeak, Hallie C. Kern, Rachael Villari, Nitsan Goldstein, Emily Lo, Albert Yeung, Lukas Richie, Bridget Skelly, Jenna Golub, Manmeet Rai, Teppei Fujikawa, Julio E. Ayala, Joel K. Elmquist, Christoph A. Thaiss, David H. Wasserman, Kevin W. Williams, Erik B. Bloss, and J. Nicholas Betley.
Leave a comment
You must be logged in to post a comment.