Marathon runners often develop irregular heartbeats as they age. UPI/Matthew Healey | License Photo
MANCHESTER, England, May 13 (UPI) -- Humans have a built-in pacemaker, but it doesn't always work properly -- which is why older patients with irregular heartbeats sometimes need an artificial one installed.
Oddly, many elderly with a history of athletic training and endurance running experience heart rhythm disturbances and require the aid of a pacemaker. Now doctors think they know why.
A new study by researchers at the University of Manchester found that the molecular properties of rodents' pacemakers were transformed in response to exercise training.
Previously, doctors had assumed that a malfunctioning pacemaker was the result of a problem with the nervous system. But this new study suggests otherwise.
"The heart rate is set by the heart's pacemaker, but this is controlled by the nervous system," explained Dr. Alicia D'Souza, one of the study's authors. "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."
"But our research shows this is not the case," Dr. D'Souza added. "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."
In other words, athletes may be training their pacemaker to become out of sync as they grow older.
Most people have a resting heart rate of somewhere between 60 and 100 beats per minute. Marathon runners can have heart rates as low as 30 beats per minute.
"Although endurance exercise training can have harmful effects on the heart," explained the study's lead researcher, Professor Mark Boyett, "it is more than outweighed by the beneficial effects."
The researchers say more work is needed before they can draw actionable conclusions about the effects of extreme exercise on a human's pacemaker.
The study was published this week in the journal Nature Communications.