Exercise does more than strengthen the heart. New research suggests it also physically reshapes the nerves that control the heart, revealing an unexpected difference between the left and right sides of the body.
Scientists from the University of Bristol (UK) have discovered that moderate aerobic exercise changes the structure of nerve cells involved in regulating heart activity. Even more surprising, the changes were dramatically different on both sides of the body. The results, published in Autonomous neurosciencecould potentially help doctors develop more precise treatments for irregular heartbeats, chest pain, angina and stress-induced “broken heart” syndrome.
The discovery was made in rats, so further research is needed to determine whether the same changes occur in humans. Nonetheless, it offers a new perspective on how physical activity influences the nervous system that keeps the heart functioning.
Exercise changes the heart’s hidden control system
The heart is regulated in part by the autonomic nervous system, a network of nerves that automatically manages essential functions such as heart rate, breathing and digestion. A branch of this system helps the heart beat faster when the body needs more oxygen, such as during exercise or in stressful situations.
Small clusters of nerve cells called stellate ganglia play an important role in this process. Located on both sides of the lower neck and upper chest, these nerve nodes send signals that influence heart rate and other aspects of heart function.
The new research suggests that regular exercise changes these nerve groups in ways that scientists had not previously recognized.
Lead author of the study, Dr Augusto Coppi, senior lecturer in veterinary anatomy at the University of Bristol, said: “The discovery reveals a previously hidden left-right pattern in the body’s ‘autopilot’ system that helps operate the heart.
“These nerve groups act as a dimmer switch for the heart and we have shown that regular, moderate exercise causes the switch on a specific side. This could help explain why some treatments work better on one side than the other and, in the future, help doctors target therapies more precisely and effectively.”
Just 10 weeks of exercise produced striking nerve changes
To study how exercise affects these nerve groups, researchers examined rats that underwent 10 weeks of moderate aerobic training. Aerobic exercise is any physical activity that increases heart rate and breathing, such as brisk walking, swimming or cycling.
The study involved researchers from University College London (UCL) in the United Kingdom, the University of São Paulo (USP) and the Federal University of São Paulo (UNIFESP) in Brazil.
The team used advanced three-dimensional analysis techniques known as stereology to examine the nerve cells. This approach allows scientists to estimate the number, size and distribution of cells in tissues.
The results revealed an unusual imbalance between the two sides of the body. In trained rats, the right cluster of cardiovascular nerves contained about four times as many neurons as the left cluster, a striking difference from the pattern seen in untrained rats.
The nerve cells also changed size, but in opposite directions. The neurons on the left almost doubled in size, while those on the right became slightly smaller.
These results suggest that exercise does not affect all of the nerves controlling the heart equally. Instead, it produces distinct structural changes on each side, potentially providing clues about how the nervous system adapts to regular physical activity.
Could this discovery lead to better heart treatments?
The findings could have important implications in treating conditions involving abnormal nerve activity around the heart.
Arrhythmias occur when the heart beats too fast, too slow, or irregularly. Angina is chest pain or discomfort usually caused by insufficient blood flow to the heart muscle. Another condition, commonly called “broken heart” syndrome, involves a sudden weakening of the heart muscle that is often triggered by intense emotional or physical stress.
In some patients, doctors treat these problems by reducing excessive nerve signals reaching the heart. Procedures such as stellate ganglion nerve blocks temporarily interrupt nerve activity, while denervation involves the disruption of certain nerve pathways.
Understanding how the left and right nerve groups differ could eventually help doctors determine which side should be targeted for the greatest benefit.
Dr Coppi explained: “Irregular heart rhythms, known as arrhythmias, stress-induced ‘broken heart’ syndrome and certain types of chest pain are often treated by reducing overactive stellate ganglia – the small, paired nerve nodes in the lower neck and upper chest region that send ‘go faster’ signals to the heart.
“By mapping how exercise changes these ganglia on each side, the study offers clues that could one day refine procedures such as nerve blocks or denervation on the side most likely to help. The results are at an early stage and in rats, so clinical studies should follow.”
What’s next for research on exercise and the heart?
Although the structural changes are substantial, scientists have yet to establish exactly how they affect heart function.
The research team plans to study whether differences between the left and right nerve groups influence the heart’s behavior at rest and during physical activity. They also intend to look for similar models in other animal models and possibly in humans.
For human studies, researchers hope to use non-invasive markers, which could provide information about nerve activity without requiring surgery or tissue sampling.
If the same left-right differences are seen in individuals, this finding could help guide more personalized treatments for arrhythmias, difficult-to-treat angina and stress-induced “broken heart” syndrome.
Dr Coppi added: “Understanding these left-right differences could help us personalize treatments for heart rhythm disorders and angina. Our next step is to test how these structural changes translate into function and whether similar patterns appear in larger animals and humans. »
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