May 15th, 2014

Exercise: Can There Be Too Much of a Good Thing?

In recent years researchers have developed a more complicated view of the relationship of health and exercise. Although observational studies have consistently shown that some physical activity is better than none, studies that have drilled deeper into the data suggest that these health benefits may be curtailed in people who exercise very frequently or very intensely. Now two new studies from Europe, published in the journal Heart, offer new support for these observations.

In the first study, Nikola Drca and colleagues analyzed data from exercise questionnaires and hospital records of nearly 45,000 Swedish men. They found that men who exercised intensively more than five hours a week at the age of 30 were more likely to develop atrial fibrillation (AF) than men who exercised less than one hour a week. Their risk was even higher if they subsequently quit exercising later in life. By contrast, men who reported more moderate exercise —  walking or bicycling more than one hour per day — had a reduced risk of AF.

In an accompanying editorial, Eduard Guasch and  Lluís Mont write that other studies have found a similar association between intense exercise at an early age and the later development of AF. They speculate that exercise that is self-reported to be intense is likely more intense in 30-year-olds than in 60-year-olds.

In the second study, Ute Mons and colleagues followed more than 1,000 patients with coronary heart disease. Overall, patients who exercised strenuously two to four days a week had the lowest risk of death and cardiovascular events. But there was an increase in risk in both the group who rarely exercised and in those who exercised every day. In their editorial Guasch and Mont speculate that intensive exercise may have a pro-inflammatory effect that may be especially harmful in some people with atherosclerotic disease.

Guasch and Mont acknowledge the limitations of observational studies based on self-adminstered questionnaires measuring physical activity. But, they write, in summary the two studies suggest that for exercise “maximum cardiovascular benefits are obtained if performed at moderate doses, while these benefits are lost with (very) high-intensity and prolonged efforts.”

Although the studies reported an excess risk beginning at five hours a week or with daily exercise, the editorialists write that this “should be considered solely as vague guidelines and might have little value in exercise counseling. In the clinical setting, an individualized mechanistic approach aiming to identify individuals at risk and detect the development of a deleterious substrate might better serve to titrate an optimal individualized dose of exercise.”


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