James Heilman, MD [creativecommons license] via Wikimedia Commons
Physical activity has many positive effects on the cardiovascular system, but intense endurance training can also be detrimental. Athletes, especially those with a long training history, are more likely to develop arrhythmias. Sinus bradycardia (a slow resting heart rate) is the most common training-associated arrhythmia. Although it is often a benign physiological adaptation to maintain normal cardiac output and blood pressure by compensating for training-induced increases in stroke volume, bradycardia can become pathological and lead to the need for electronic pacemaker implantation.
Lab Anim. 43, 223 (2014).
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