Ten weeks of moderate aerobic exercise reshaped nerve clusters that help control the heart in rats, revealing a surprising split between the body’s left and right sides. The University of Bristol-led research suggests that these paired control centers do not adapt to training in the same way.
The findings could eventually help researchers refine treatments for irregular heart rhythms and certain types of chest pain. But this is an early-stage animal study, not evidence that the same changes occur in people or that a new treatment is ready for patients.
The nerve hubs helping run the heart
The researchers focused on the stellate ganglia, two small nerve hubs located in the lower neck and upper chest. These clusters send signals that can speed up the heart, making them part of the automatic control system that keeps it responding to the body’s demands.
“These nerve clusters act like the heart’s dimmer switch,” Bristol researcher Dr. Augusto Coppi said in the university’s September 24, 2025, announcement. His comparison highlights the study’s central idea that exercise may remodel the controls, rather than affecting only the heart muscle itself.
That distinction shifts attention away from the pump and toward the nerves helping regulate it. More specifically, the team wanted to understand whether training changed the structures of the left and right nerve clusters differently, something that had remained unclear.
What changed after 10 weeks
The project brought together researchers from Bristol, University College London, the University of São Paulo, and the Federal University of São Paulo. Using three-dimensional quantitative methods called stereology, the team examined nerve clusters from trained and untrained rats to assess how their structure differed. This was a look at adaptation over weeks, rather than a snapshot of the heart beating faster during a workout.
After 10 weeks of treadmill exercise, trained rats had roughly four times as many neurons in the right stellate ganglion as in the left. That imbalance was absent in untrained animals, so the fourfold figure describes a right-to-left comparison rather than a fourfold increase across the entire nerve network.
Cell size also moved in opposite directions. The study reported a 1.8-fold increase in neuron volume on the left, nearly doubling, while neurons on the right became slightly smaller. Together, the findings reveal a more complicated response than simply growing more or bigger nerve cells everywhere.
Why the difference could matter for treatment
Why should it matter which side changes? Coppi pointed to procedures that reduce activity in overactive stellate ganglia, which may be relevant to conditions including arrhythmias, stress-induced “broken-heart” syndrome, and difficult-to-treat angina.
The researchers suggest that mapping these left-right adaptations could eventually help refine nerve blocks or denervation procedures. Rather than treating the paired nerve hubs as interchangeable, doctors might one day have better evidence for choosing which side to target.
For now, that remains a possibility, not a demonstrated clinical benefit. The study offers a reason to investigate more precisely targeted care, but it does not establish which side would be best for a particular patient or condition.
Different nerve structures do not tell the whole story
A larger nerve cell is not, by itself, proof of better heart function. Likewise, finding more neurons on one side does not establish how strongly that nerve cluster signals or what the difference means for an individual heartbeat.
The researchers explicitly identified that missing connection as a priority for follow-up work. Their next task is to link the structural changes to how the heart behaves, rather than assuming that the appearance of the nerve clusters explains their function.
For readers, the practical distinction is between discovering a possible biological mechanism and proving a treatment works. These results do not provide a human exercise prescription or show that training can replace treatment for a heart rhythm disorder.
What researchers need to test next
The team plans to investigate how the observed changes relate to heart function both at rest and during exercise. That should help clarify whether the left-right pattern has a meaningful role in the heart’s response to physical activity.
Researchers also want to look for similar patterns in larger animals and in humans using noninvasive markers. Finding comparable changes would be an important step, but testing whether that knowledge improves treatment would still require clinical research.
The intriguing possibility is that understanding exercise means looking beyond the heart muscle to the nerve network helping direct it.
The study was published in Autonomic Neuroscience.
