Science Says Excessive Endurance Training Too Much of a Good Thing

Ultrarunner Micah True, known to many as Caballo Blanco, died in March on a training run. Was his death indicative of the dangers of ultrarunning? Science takes a look.

The old saying, “there is too much of a good thing” may actually hold some truth. On March 27, 2012, a 58 year-old ultramarathoner named Micah True died suddenly while on a 12-mile training run. If you read Born to Run you know Micah True by his other name, Caballo Blanco. True followed extreme running routines, and would run as far as 100 miles in one day. The autopsy of his heart revealed it was enlarged and scarred. It was determine the cause of his death was due to lethal arrhythmia, or irregular heart rhythm. The case suggests True’s heart problem may have been results of “Phidippides cardiomyopathy.”1

Phidippides was a Greek messenger who suddenly died after running more than 175 miles in two days. When hypertrophic cardiomyopathy (when the heart muscle becomes thick), anomalous coronary arteries (malformation of coronary vessels), and coronary atherosclerosis (progressive disease where atherosclerotic changes occur in the walls of coronary arteries) have been excluded from causes of death “Phidippides cardiomyopathy” is often dubbed primary reason for demise.2

Dr. James O’Keefe, of Saint Luke’s Hospital of Kansas City, Missouri, conducted research that suggests extreme endurance training can cause transient structural cardiovascular changes and elevations of cardiac biomarkers. These changes return to normal within a week. Some individuals who continuously train this way for months, however, experience repetitive injury to the heart that can lead to the formation of patchy myocardial fibrosis. Myocardial fibrosis is a condition that involves impairment of the muscles of the heart. It is a form of fibrosis, which means that the scar tissue of the heart hardens, making it inflexible, and can ultimately lead to heart failure.3 In one study, approximately 12% of marathon runners showed evidence of myocardial scarring, and the coronary heart disease event rate during a two year follow up was significantly higher than in controls.4

“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,” said Dr. O’Keefe. “However, as with any pharmacologic 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.”5

As with the Golden Mean suggested by the Greeks, there is an amount of any physical activity that carries the most benefit and least harm. As is possible with Micah True, ultrarunners may be testing that line regularly.

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