Washington: A new research from the University of Manchester has found as to why athletes are more likely to have abnormal heart rhythms.
Elderly athletes with a lifelong history of training and competing in endurance events like marathons, triathlons and iron man challenges can have heart rhythm disturbances, known as arrhythmias.
The Manchester research in rodents, funded by the British Heart Foundation, shows molecular changes in the heart's pacemaker occur in response to exercise training.
The finding overturns the commonly held belief that an increased activity of the autonomic nervous system causes this specific reaction to endurance training.
While normal adults have resting heart rates between 60-100 beats per minute, hearts of endurance athletes can beat only 30 times per minute or even lower at night time when there can be long pauses between heart beats.
"The heart rate is set by the heart's pacemaker, but this is controlled by the nervous system. The 'vagal' nerves lower the heart rate and therefore it was assumed the low heart rate of athletes is the result of over activity of the vagal nerves," Dr Alicia D'Souza, from The University of Manchester and first author on the paper, said.
"But our research shows this is not the case. Actually the heart's pacemaker changes in response to training and in particular there is a decrease in an important pacemaker protein, known as HCN4, and this is responsible for the low heart rate," she added.
The researchers say these molecular changes in the sinus node - the cardiac structure responsible for generating heart rhythm - may help us to understand the more frequent occurrence of heart rhythm disturbances or even loss of consciousness in athletes.
The findings are published in the journal Nature Communications.