Exercise Can "Reprogram" the Heart — Scientists

Regular aerobic training reshapes not only the heart but also the nerve clusters that control it, with the right and left sides responding in entirely different ways. This unexpected conclusion was reached by an international team of scientists led by researchers from the University of Bristol after conducting a series of experiments on rats. The results were published in the journal Autonomic Neuroscience.

The focus of the study was the stellate ganglia — paired clusters of sympathetic nervous system cells located in the lower neck and upper chest. These are the structures that send signals helping the heart adjust to physical exertion, including by accelerating its contractions.

Over the course of ten weeks, the experimental animals performed moderate aerobic exercises on a treadmill. After the program was completed, the scientists conducted a detailed three-dimensional analysis and stereological examination of the nerve clusters, assessing the number and size of neurons as well as the volume of the ganglia. The results from the trained rats were compared with data from their untrained counterparts.

The findings were striking: in the right ganglion of the trained animals, the neuron count was approximately four times greater than in the left. No such asymmetry was observed in the control group rats. It is important to clarify that this refers specifically to the difference between the two sides of the body, rather than a fourfold increase in the total number of cells as a result of exercise.

Neuron sizes also changed unevenly: on the left side, cells became nearly twice as large, whereas on the right, they slightly decreased in size. The nervous system, therefore, adapted to physical exercise in a markedly asymmetric manner.

According to the authors, the identified differences may have significant implications for understanding the neural regulation of the heart. In certain rhythm disorders and a number of other conditions, doctors deliberately target excessive activity of the stellate ganglia. Knowledge of the specific characteristics of the right and left ganglia could, in the future, help in more precisely selecting therapeutic targets.

However, for now, these are structural changes documented in animals. Their specific impact on cardiac function has yet to be determined, as does whether similar reorganization occurs in the human body.