Exercise is known to boost your energy, improve your mood, combat calories, benefit your overall health, and even enhance your sex life. Surprisingly, two separate teams of researchers recently discovered that more exercise isn’t always better. In fact, greater intensity and longer duration does not always increase the benefits of exercise — especially when it comes to the cardiovascular system — and your age may also influence potential heart health advantages produced by physical activity. “It remains unknown why some individuals develop deleterious effects when engaged in regular training while others remain unaffected,” wrote the authors of an editorial published in the British Medical Journal. “Exercise intensity, as well as the type of exercise, is clearly a major determinant.”

More Doesn't Always Mean Better

The current recommendation for heart disease patients is that they should do up to an hour of moderate aerobic exercise at least five times a week. In a new German study, the team of researchers tracked the frequency and intensity of physical activity and the survival of more than 1,000 people with stable coronary artery heart disease over the course of 10 years. All of the participants, most were in their 60s, had attended a rehabilitation program to help them exercise regularly and ward off a further heart attack or stroke. Overall, one in 10 said they rarely or never did any exercise, while about 40 percent were physically active two to four times weekly. About a third (30 percent) of the study participants did more, while the exact same amount did less.

After taking into account other influential factors, the most physically inactive were around twice as likely to have a heart attack/stroke as those who were regularly physically active. And they were around four times as likely to die of cardiovascular and all other causes. Surprisingly, though, those who did the most strenuous daily exercise were also more likely to die of a heart attack/stroke — in fact, their odds of dying doubled.

A Matter of Age

In the Swedish study, the researchers quizzed more than 44,000 men between the ages of 45 and 79 about their physical activity patterns at set ages: 15, 30, 50, and during the past year. From 1997 onwards, participants' heart health was tracked for an average of 12 years to gauge how many developed an irregular heartbeat or atrial fibrillation, a risk factor for stroke. Those who cycled or walked briskly for an hour a day or more at the age of 60 were around 13 percent less likely to develop atrial fibrillation (AF) than those who did virtually no exercise at all. Yet, the men who exercised intensively for more than five hours a week were 19 percent more likely to develop the condition by the age of 60, compared to those exercising less than an hour a week. More dramatically, the risk level rose to 49 percent among the men who exercised more than five hours a week when they were 30 and then did less than an hour by the time they were 60.

“Leisure-time exercise at younger age is associated with an increased risk of AF, whereas walking/bicycling at older age is associated with a decreased risk,” concluded the authors.

Sources: Mons U, Hahmann H, Brenner H. A reverse J-shaped association of leisure time physical activity with prognosis in patients with stable coronary heart disease: evidence from a large cohort with repeated measurements. British Medical Journal. 2014.

Drca N, Wolk A, Jensen-Urstad M, Larsson SC. Atrial fibrillation is associated with different levels of physical activity at different ages in men. British Medical Journal. 2014.