KANSAS CITY, MISSOURI. Several studies have concluded that moderately vigorous exercise is healthy, whilst prolonged, strenuous exercise is not. A study involving 100 German marathon runners over the age of 50 years found that coronary calcification was far more pronounced in the runners than in healthy controls not engaged in strenuous, sustained exercise. A Danish study recently concluded that athletes who regularly engaged in intense physical endurance sports had a 5 times greater risk of developing atrial fibrillation (AF) than did less vigorously exercising or sedentary controls. A study involving 17,000 male physicians in the USA concluded that regular jogging was associated with a 53% increased risk of developing AF in all age groups, with those jogging in excess for 4 miles a day having the greater risk.

Now a group of American medical doctors interested in sports medicine provide a prescription for just the right amount of exercise. They emphasize that too little exercise is still the major public health problem, but caution that too much exercise can have serious adverse consequences. There is evidence that higher "dosages" of running are not necessarily healthier. Maximal benefit is achieved from moderate-to-vigorous exercise (fast walking or slow jogging) for approximately 40 minutes. On the other hand, running marathons or even half-marathons is likely to do serious damage to the heart, a condition the authors name "cardiac overuse injury". Cardiac overuse injury may involve premature aging of the heart, arrhythmia, accelerated coronary atherosclerosis, and even sudden cardiac death.

The authors conclude that "more" is probably not "better" when it comes to exercise, and participants should not harbour the illusion that if one hour of vigorous activity is good for health, then doing 4 hours of strenuous physical activity will multiply the health benefits. Accumulating data suggests that it does just the opposite – destroys the protective health benefits of exercise. They suggest the following "prescription" for exercise:

• Run 2 or 3 miles at a comfortable pace 2 to 4 times a week.
• Make swimming a regular part of activity. Lift weights or do other strength training 2 or 3 times weekly.
• Do yoga or some other stretching exercises regularly.
• Walk or garden as much as your heart desires.

Bhatti, SK, Hagan, JC, et al. The lady doth protest too much, methinks. Missouri Medicine, Vol. 110, January/February 2013, pp. 17-20

Editor's comment: For more on the benefits/dangers of endurance exercise, see my research report Endurance Exercise – Is it Worth it?