Regular moderate aerobic exercise does more than strengthen the heart muscle, according to a new study: it appears to physically reshape the nerve clusters that regulate how the heart beats, and does so differently depending on which side of the body they sit.
Researchers led by Dr. A. Augusto Coppi at the University of Bristol, working with colleagues at University College London and two Brazilian universities, put rats through 10 weeks of moderate aerobic training and then examined their stellate ganglia, paired clusters of nerve cells near the base of the neck that help control heart rate and rhythm. Using a 3D analysis technique called stereology to count and measure individual neurons, the team found that trained rats developed a right stellate ganglion with roughly four times as many neurons as the left — a lopsided pattern not seen in untrained animals. Neurons on the left side, meanwhile, nearly doubled in size, while those on the right grew slightly smaller.
"The heart's dimmer switch"
"These nerve clusters act like the heart's dimmer switch," Coppi said, describing how the left and right stellate ganglia exert different, asymmetric influence over heart rhythm and contraction strength. The study, published in the journal Autonomic Neuroscience, is the first to show that exercise training reshapes the two sides of this nerve network so differently, rather than simply strengthening both in tandem.
The researchers say the findings, while preliminary, point toward a possible future where doctors could target one side of the stellate ganglion rather than the other when treating conditions such as arrhythmias, angina or stress-induced "broken-heart" syndrome, using techniques like nerve blocks or selective denervation that are already used in some heart patients today. "The findings are early-stage and in rats, so clinical studies would need to follow," Coppi cautioned, noting that the asymmetric remodeling has not yet been confirmed in humans and that any clinical application remains a distant prospect rather than an immediate treatment option.
