Too much exercise can be bad for your heart, two new studies have warned.
Research by German scientists found overdoing high intensity exercise may actually increase the risk of death from a heart attack or stroke in those with existing heart disease.
And a Swedish study, also published online in the journal Heart, suggests that 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.
The studies support research released yesterday which showed that young men who run marathons are more likely to need pacemakers in old age.
Both sets of new findings indicate that more does not always mean better when it comes to the health benefits of exercise, 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.
All the participants, most of whom were in their sixties, had attended a cardiac rehabilitation programme to help them exercise regularly and ward off a further heart attack or stroke.
Current guidance recommends that heart disease patients should do up to an hour of moderate intensity aerobic activity at least five times a week.
Around 40 per cent were physically active two to four times weekly, 30 per cent did more and 30 per cent did less. Overall, one in 10 said they rarely or never did any exercise.
After taking account of other influential factors, the most physically inactive were around twice as likely to have a heart attack or stroke as those who were regularly physically active. And they were around four times as likely to die of cardiovascular disease and all other causes.
However, surprisingly, researchers found those who did the most strenuous daily exercise were also more than twice as likely to die of a heart attack or stroke.
In the Swedish study, the researchers questioned more than 44,000 45 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.
Their heart health was tracked for an average of 12 years from 1997 onwards to gauge how many developed
They found that men who had exercised intensively for more than five hours a week were 19 per cent more likely to have developed the condition by the age of 60 than those exercising for less than one hour a week.
The level of risk rose to 49 per cent 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.
However, those who cycled or walked briskly for an hour a day or more at the age of 60 were around 13 per cent less likely to develop an irregular heartbeat than those who did virtually no exercise at all.
of 30 than it is at the age of 60, so may have less extreme effects on the body.
Dr Lluis Mont, of the Hospital Clinic de Barcelona in Spain, said: ‘Maximum cardiovascular benefits are obtained if performed at moderate doses, while these benefits are lost with [very high] intensity and prolonged efforts.’
However, Dr Mont emphasised that not exercising at all is bad for our long term health, adding: ‘A thin line separates accurate information and unnecessary alarmism, leading to inactivity and consequent heart disease.
‘The benefits of exercise are definitely not to be questioned, on the contrary, they should be reinforced.
‘The studies, and future studies, will serve to maximise benefits obtained by regular exercise while preventing undesirable effects – just like all other drugs and therapies.’
Just yesterday another study revealed that running marathons can be bad for the heart.
Researchers at the University of Manchester found that people who take part in extreme sporting challenges when they are young are more likely to need pacemakers in old age.
Tests on mice, funded by the British Heart Foundation, showed microscopic changes take place in the body due to exercise training.
This can disrupt the electrical pulse of the heart, causing the super-fit to suffer abnormal heart rhythms.