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There may be a limit to benefits of exercise, according to new studies that found too much exercise is actually bad for the heart.
In one study, researchers in Sweden surveyed more than 44,000 men ages 45 to 79 about their exercise patterns over the past years, and then tracked their heart health for an average of 12 years.
They found that men who had exercised intensely for more than five hours a week at age 30 were 19 percent more likely to have developed an abnormal heartbeat condition called atrial fibrillation by age 60, compared with men who exercised for less than one hour a week.
In atrial fibrillation, the heart beats irregularly and often rapidly, which can cause poor blood flow to the body and increase the risk of stroke.
In the other study, researchers in Germany looked at about 1,000 people in their 60s who had heart conditions and had enrolled in an exercise program to improve their heart health.
The researchers followed the participants for 10 years and found that people who were the least active, as well as those who did daily, high-intensity exercise, had a higher risk of death from a heart attack or stroke than people in the middle.
The lowest risk of dying of a heart attack or stroke was seen in the patients who exercised strenuously for two to four days a week. [7 Common Exercise Errors And How to Fix Them]
Both studies were published May 14 in the journal Heart.
The new findings suggest that people get maximum benefits from physical activity if they exercise moderately, according to Dr. Lluís Mont, of Hospital Clínic de Barcelona, and a colleague who wrote an editorial that accompanied the studies.
The studies also point to a delayed effect of intense exercise on the heart, Mont wrote. The researchers found that men who did more than five hours of intense exercise weekly at age 30 and had stopped their training in middle age, wound up having a nearly 50 percent higher risk of developing an irregular heartbeat when they were 60.
Conversely, men older than 50 who did a similar intense pattern of exercise didn't show the same increase in risk. Men who cycled or walked briskly for at least an hour daily at age 60 were 12 percent less likely to develop atrial fibrillation than those who did no exercise at all.
"The benefits of exercise are definitely not to be questioned; on the contrary, they should be reinforced," Mont and his colleague wrote. But the new findings and future studies "will serve to maximize beneﬁts obtained by regular exercise while preventing undesirable effects—just like all other drugs and therapies."