Two studies in the British journal Heart add new evidence to the case that extreme amounts of exercise may be detrimental to health.
One study followed 1,038 patients with heart disease for 10 years and found that those who vigorously exercised daily were more than twice as likely to die of a heart attack or stroke than those who exercised only two to four days a week, while those who exercised rarely or never had the worst outcomes.
That finding is startling because current medical recommendations call for heart-disease patients (like everyone else) to exercise five to seven days a week. Those recommendations aren't likely to change on the basis of a single study, especially one drawn from potentially unreliable patient reports of how much they exercise.
The second study adds to already substantial evidence that endurance exercise increases the risk of atrial fibrillation, a generally non-life-threatening cardiac arrhythmia that greatly increases the risk of stroke. This finding parallels that of a previous study that found a 74 percent increase in the risk of atrial fibrillation in men younger than 50 who exercised vigorously five to seven days a week.
The two studies will intensify debate within sports medicine about the health implications of endurance athletics such as serial marathon running.