Cardiologists publishing Monday in a peer-reviewed journal reported that sustained marathon training produces measurable structural changes in the hearts of amateur runners. The findings coincide with record participation in autumn races across Europe and North America, prompting calls for wider pre-race cardiac screening.

The research, led by investigators studying middle-aged recreational athletes, found that repeated high-volume endurance training enlarged left-ventricular chambers and altered heart-rate variability. The authors said the adaptations were largely benign but warned a small subset of older runners showed markers associated with atrial fibrillation and coronary calcification.

Marathon entries have climbed sharply, with organisers of major events reporting oversubscribed ballots and rising numbers of first-time entrants over 40. Recent coverage has highlighted the sport's psychological appeal alongside its physical demands, sharpening scrutiny of cardiac risk among untrained participants.

The British Heart Foundation and the American Heart Association have previously urged runners with symptoms such as chest pain or palpitations to seek evaluation before endurance events. Cardiologists quoted in the study recommended baseline screening for entrants over 40 and those with family histories of heart disease.

"Endurance exercise is overwhelmingly protective, but the heart adapts, and in a minority those adaptations carry risk," the study's lead author said. "Screening for older first-time marathoners is a sensible precaution as participation grows."