How much is too much exercise?

NEW research has found that competitive running increase your risk of an acute event, and running more than 6.5 kilometres a day is dangerous to your health.

Some of the more than 80,000 registered runners race up Williams Street in Sydney, Sunday, Aug. 10, 2014, at the start of the City 2 Surf annual fun run. Competitors are running the 14 km (8.7 mile) course raising millions of dollars for charities. (AP Photo/Rick Rycroft)

THE death of 27-year-old Sydney man Chris Head during the City2Surf over the weekend has brought into sharp focus the dangers of marathon running.

Now, new research has found that not only do competitive running events increase your risk of an acute event, but that running more than 6.5 kilometres a day could be dangerous to your health.

More: City2Surf runner dies

The new study examined how much exercise is too much. Researchers focused on 2,400 heart attack survivors and found that the more exercise they did, the less risk they faced of dying from heart disease — up to a point.

Benefits began to decline among those who ran more than 48 kilometres per week.

Among walkers, the turning point, when benefits were lost, was seen in those who did more than 74 kilometres per week, or 10.5 kilometres per day.

Even more, there was a statistically significant cardiovascular risk associated with the highest levels of exercise.

“Results suggest that the benefits of running or walking do not accrue indefinitely and that above some level, perhaps 30 miles per week of running, there is a significant increase in risk,” the study said.

“Competitive running events also appear to increase the risk of an acute event.”

Thousands of runners take part in the annual City2Surf road race in Sydney on August 10, 2014.

However, researchers from the study, which was led by Paul Williams of the Lawrence Berkeley National Laboratory and Paul Thompson of the Department of Cardiology at Hartford Hospital, cautioned that since their study focused on heart attack survivors, their results might not be applicable to the population at large.

Experts generally recommend two and a half hours of moderate exercise each week, or 75 minutes weekly of vigorous exercise for a healthy heart and body.

“For patients with heart disease, almost all should be exercising, and generally most should be exercising 30-40 minutes most days,” said Carl Lavie, a cardiologist at the John Ochsner Heart and Vascular Institute in New Orleans.

“But from a health standpoint, there is no reason to exercise much longer than that and especially not more than 60 minutes on most days.”

Running more than four miles a day could be dangerous to your health.

The research was published in the peer-reviewed journal Mayo Clinic Proceedings.