Micah True, a legendary marathon runner, died suddenly while on a routine 12-mile training run in March.
The pathological changes in the heart of the 58 year-old athlete may have been the outcome of "Phidippides cardiomyopathy," a condition caused by chronic excessive endurance exercise.
Studies show that competing in extreme endurance exercise such as marathons, iron man distance triathlons, and very long distance bicycle races may cause structural changes to the heart and large arteries, damaging them, the journal Mayo Clinic Proceedings reports.
"Physical exercise, though not a drug, possesses many traits of a powerful pharmacologic agent. A routine of daily physical activity can be highly effective for prevention and treatment of many diseases, including coronary heart disease, hypertension, heart failure and obesity," says James H. O'Keefe of Saint Luke's Hospital of Kansas City.
"However, as with any pharmacologic (drug) agent, a safe upper dose limit potentially exists, beyond which the adverse effects of physical exercise, such as musculoskeletal trauma and cardiovascular stress may outweigh its benefits," adds O'Keefe.
For some individuals, over months and years of repetitive injury, this process can lead to the development of patchy myocardial fibrosis or scarring of the heart tissues, according to a St Luke's Hospital statement.
In one study, the coronary heart disease rate during a two-year follow up was significantly higher in marathon runners than in those who never took part in extreme exercises.
Life-long vigorous exercisers generally have low mortality and disability rates and excellent functional capacity, O'Keefe notes.