Overdosing on high intensity exercise may actually increase the risk of death from a heart attack or stroke in those with existing heart disease, according to German research in the journal Heart.
And a second study by Swedish researchers suggests young men undertaking endurance exercise for more than five hours a week may increase their risk of developing an irregular heart rhythm in later life.
Both sets of findings indicate more exercise doesn’t always mean better and raise questions about the intensity and duration of physical activity at different times of life.
In the German study, the researchers tracked the frequency and intensity of physical activity and the survival of more than 1,000 people with stable coronary artery heart disease for 10 years.
These people aged in their 60s attended a cardiac rehabilitation program to help them exercise regularly and ward off a further heart attack or stroke.
Current guidance recommends heart disease patients should do up to an hour of moderate intensity aerobic activity at least five times a week. Around 40% were physically active 2 to 4 times weekly; 30% did more; 30% did less. Overall, one in 10 said they rarely or never did any exercise.
After taking account of other 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.
But those who did the most strenuous daily exercise were also more than twice as likely to die of a heart attack/stroke, the findings show.
In the Swedish study, the researchers quizzed more than 44,000 45-year-old to 79-year-old men about their leisure time physical activity patterns at the ages of 15, 30, 50, and during the past year, when their average age was 60.
Participants’ heart health was tracked for an average of 12 years from 1997 onwards to gauge how many developed an irregular heartbeat, a known risk factor for stroke.
They found that men who had exercised intensively for more than five hours a week were 19% more likely to have developed the condition by the age of 60 than those exercising for less than one hour a week.
This level of risk rose to 49% among those who did more than five hours of exercise a week at the age of 30, but who subsequently did less than an hour by the time they were 60.
But those who cycled or walked briskly for an hour a day or more at the age of 60 were around 13% less likely to develop atrial fibrillation than those who did virtually no exercise at all.
While perceptions on how much exercise is good may be changing, the fact remains that none is bad for long term health, the researchers say.
“A thin line separates accurate information and unnecessary alarmism, leading to inactivity and consequent heart disease,” the researchers write.
“The benefits of exercise are definitely not to be questioned; on the contrary, they should be reinforced. The studies reviewed here, and future studies, will serve to maximise benefits obtained by regular exercise while preventing undesirable effects—just like all other drugs and therapies.”
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