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Heart Health

High-intensity exercise might actually be BAD for you

If you have too much of it, it could be bad for your heart – particularly if you have existing heart conditions, even if you were on an exercise programme.

THOUGHT THAT HIGH intensity exercise could be the best way to boost your health?

It turns out that if you get too much of it, it could be very bad for your heart. That’s according to two studies that indicate that when it comes to physical activity, more doesn’t always mean better.

In fact, prolonged high intensity exercise risks heart health, with one study looking at people who have existing heart disease. A second study looked at older men and high intensity exercise.


Overdosing on high intensity exercise may actually increase the risk of death from a heart attack or stroke in those with existing heart disease, suggests German research which is published online in the journal Heart.

In addition, a second Swedish study in the journal 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.

J-shaped curve

Both sets of findings indicate a “J-shaped curve” for the health benefits of exercise.

This means that more is not always better.

In the German study, the researchers tracked the frequency and intensity of physical activity and the survival of more than 1000 people with stable coronary artery heart disease for 10 years.

All the participants, most of whom were in their 60s, had attended a cardiac rehabilitation programme to help them exercise regularly.

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 2-4 times weekly
  • 30 per cent did more; 30 per cent did less.
  • 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/stroke as those who were regularly physically active. And they were around four times as likely to die of cardiovascular and all other causes.

However, those who did the most strenuous daily exercise “were also more than twice as likely to die of a heart attack/stroke”.

Swedish study

Meanwhile, in the Swedish study, more than 44,000 45-79 year old men were asked 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.

The participants’ heart health was tracked for an average of 12 years from 1997 onwards to see how many developed an irregular heartbeat or atrial fibrillation (the latter is a risk factor for stroke).

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.

This 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 did less than an hour by age 60.

The men who cycled or walked briskly for an hour a day or more at age 60
were around 13 per cent less likely to develop atrial fibrillation than those who did virtually no exercise.


In an editorial, Spanish authors suggest that this might be because the intensity of exercise is likely to be greater at the age of 30 than it is at the age of 60, so may have less extreme effects on the body.

They say that while it seems “counterintuitive” to think that physical activity could aggravate heart disease, other smaller studies have also suggested this possibility. They note that endurance training in particular is linked to an acute (reversible) pro-inflammatory state.

Genes may also have an important role in determining the ‘safety threshold,’ they to suggest.

The experts add: “The benefits of exercise are definitely not to be questioned; on the contrary, they should be reinforced.”

Read: One in three Irish adults never exercise>

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