- A rat study has found that aerobic exercise may reshape nerves that control the heart.
- However, the impact was not the same on both sides of the stellate ganglia.
- These findings could pave the way for improvements in nerve-targeted therapies, but human studies are still needed.
- Experts say this research adds more proof of aerobic exercise’s heart health benefits.
Scientists have long known that regular exercise can lower your heart rate and strengthen your cardiovascular system.
However, new research on rats suggests that aerobic workouts may also reshape part of the body’s nervous system.
After 10 weeks of moderate treadmill training, the rats’ right-side ganglion showed a large jump in neuron numbers but a shrinkage in neuron size, while the left-side ganglion saw the opposite, with fewer changes in number but an increase in neuron size.
This side-to-side difference hints that exercise might prompt the autonomic nervous system to adapt in more complex, asymmetrical ways than previously thought, according to the authors.
This could potentially open doors to new treatments for heart rhythm problems and other conditions that involve nerve control of the heart.
To learn how exercise might alter the structure of the stellate ganglia, researchers worked with Wistar rats, a common laboratory strain known for its reliability in physiological studies.
The animals were divided into trained and untrained groups.
The trained rats followed a moderate-intensity aerobic program composed of running on a treadmill for 10 weeks. This level of exercise has previously been shown to lower heart rate without changing blood pressure in rats.
After the training period, scientists examined both the left and right stellate ganglia from each animal. These clusters of nerves sit on both sides of the neck, just in front of a deep neck muscle, and serve as an important connection between the brain and the heart.
To get a detailed look at their structure, the team used advanced three-dimensional imaging combined with stereological methods, a type of quantitative microscopic analysis that allows researchers to measure volumes, cell counts, and cell sizes with mathematical accuracy.
The researchers measured three main factors: total neuron count (the number of nerve cells in each ganglion), mean neuronal volume(the average size of each neuron), and overall ganglion volume (the total size of the ganglion structure).
Four experimental groups were studied: untrained left stellate ganglion, trained left stellate ganglion, untrained right stellate ganglion, and trained right stellate ganglion
This helped them link any changes in ganglion structure to possible effects on heart function.
The differences between trained and untrained rats — and between the left and right sides — were pronounced.
In untrained animals, the left and right stellate ganglia were fairly symmetrical in neuron count and size.
However, in trained rats, the right ganglion contained four times as many neurons as the left ganglion.
In addition, there were notable changes in neuron size. In the right ganglion of trained rats, neurons were smaller — about 1.2 times smaller than in untrained rats — an indication of atrophy.
On the left side, however, neurons were larger — about 1.8 times bigger than in untrained rats — showing hypertrophy.
Ganglion volume also changed with exercise, and again, the changes depended on the side of the body. In trained rats, left-side ganglion volume decreased slightly (about 1.04-fold smaller), while right-side ganglion volume shrank more substantially (about 1.4-fold smaller).
Further, these structural shifts occurred alongside a measurable change in heart rate. Trained rats had a significantly lower heart rate — about 280 beats per minute compared to 314 beats per minute in untrained rats — while blood pressure readings (SBP, DBP, MAP) remained virtually unchanged.
The authors additionally noted that under the microscope, both sides of the stellate ganglia displayed clusters of neurons separated by nerve fibers, blood vessels, and connective tissue septa.
However, the trained animals had more prominent connective tissue septa, hinting at possible remodeling of the ganglion’s internal framework alongside changes in neuron size and number.
Taken together, the results reveal that moderate aerobic exercise doesn’t just affect the heart directly — it reshapes the nerve centers that control it, and does so in different ways depending on which side of the body they’re on.
This asymmetric neuroplasticity challenges the traditional view that exercise-induced nerve adaptations are uniform, and suggests that the autonomic nervous system may fine-tune its responses based on side-specific roles in heart regulation.
Lead study author Augusto Coppi, MD, senior lecturer in veterinary anatomy at the University of Bristol, explained that if the right-left differences are confirmed in humans, clinicians could better personalize nerve-targeted therapies for arrhythmias, pain syndromes, or dysautonomia.
It could additionally help us refine cardiac rehabilitation by leveraging exercise as a non-drug “neuromodulator.”
“The paper also notes real-world relevance of stellate interventions (blocks/denervation) in human heart rhythm disorders and other conditions, underscoring why knowing which side does what could matter clinically,” Coppi told Healthline.
He added, however, that more research is needed before we can put this information into action.
Researchers will need to map out the “wiring” behind these changes, he said, and they will need to look at the molecular drivers that explain why the left and right sides adapt differently.
Finally, these findings will need to be tested in human studies to see whether changes on one side versus the other actually affect nerve activity and heart health, which could guide exercise programs and targeted treatments, said Coppi.
Raj Dasgupta, MD, chief medical advisor for Garage Gym Reviews, who was not involved in the research, commented on the study, saying that this research is “a big deal” because it could change how we approach certain heart conditions. Dasgupta wasn’t involved in the study.
“Right now, some treatments target the nerves around the heart, and knowing that exercise reshapes them differently on each side could make those treatments more precise and effective,” he said.
Dasgupta additionally said that it could open the door to tailored exercise plans to improve heart health in specific ways.
For now, though, he said the takeaway is to keep moving.
“Regular aerobic exercise is still one of the best things you can do for your heart, and this research just gives us another reason why,” said Dasgupta.
“Beyond that, it’s too early to make medical changes based on this study, but it’s exciting to think about where the science could take us in the future.”
