Cardiology: Why a trained heart beats slower

Molecular changes in the heart may be responsible for the low resting pulse rate of elite athletes, reports a rodent study in Nature Communications this week. The finding overturns the commonly held believe that an increased activity of the autonomous nervous system caused this specific adaptation of the heart to endurance training.

While normal adults have pulse rates between 60-100 beats per minute, hearts of endurance athletes are known to beat only 30 times per minutes (or even less when asleep). Mark Boyett and his team show that exercise training of rats alters the expression of ion channels in the sinus node - the cardiac structure responsible for generating heart rhythm. These changes, and the low resting heart rate, persist even in the absence of stimulation from the autonomous nervous system, which has so far been thought to repress rhythm generation at the sinus node in the context of regular exercise.

The researchers say these molecular changes in the sinus node may help us to understand the more frequent occurrence of heart rhythm disturbances, or even loss of consciousness, in athletes.