9 January 2010 | NewScientist | 37

Jogging can kill you“Look at Jim Fixx!” cry the couch potatoes, citing the celebrity runner credited with kick-starting the jogging craze in the 1970s. At the age of 52, Fixx famously dropped dead from a heart attack midway through a run. Could exercise be a killer lying in wait for the unwary?

The risk of a heart attack does rise during vigorous exercise like jogging or shovelling snow. But the extent of the rise depends heavily on how accustomed you are to that exercise. For someone who is completely unfit, the risk can rise by as much as 100-fold, relative to when they are resting. For someone who regularly runs five times a week, their risk while exercising roughly doubles. The lesson, says David Stensel, an exercise physiologist at Loughborough University in the UK, is to be careful when you take up exercise. He advises gradually building up the intensity and duration of your exercise sessions, and that you have a medical check-up if you are over 35 and are not

used to regular physical activity.Stensel points out that the raised

risk, which lasts for the duration of the exercise and up to half an hour after it, pales into insignificance beside the overall lifetime benefits of regular exercise. Study after study has shown that keeping active lowers an individual’s risk of suffering a heart attack by 50 to 80 per cent.

That protective effect stays with you day and night – whether you are running a marathon or asleep in bed. There are a myriad other health benefits too. “You’re far better off exercising than worrying about your risk of heart attack during exercise,” says Stensel.

Is pumping iron really necessary?Look around most gyms and you’ll

probably conclude that if you don’t pump

iron you’re not doing a complete workout.

But is that really true?

Several studies have suggested a

link between muscle strength and living

longer, but for a long time it was unclear

whether other factors were confusing

the picture. People who are muscular are

more likely to be thin, aerobically fit and

generally healthy – all features known

to extend lifespan.

In the past few years, however, some

large, well-designed studies have settled

the question. One study, published in

2008, measured the muscle strength of

almost 9000 American men and followed

their health for 20 years. The death

rates among those whose muscle

strength was in the bottom third for

their age group was around 30 per cent

higher than for the other two-thirds ( BMJ,

vol 337, a439).

That link remained even after the

results had been adjusted to take

account of the effects of aerobic fitness.

“The bottom line is that both strength

and aerobic fitness make independent

contributions to health,” says Steve Blair,

one of the study’s co-authors, based at

University of South Carolina’s Arnold

School of Public Health, who helped write

the US national guidelines on exercise.

In the 2007 update of its own

recommendations on exercise, the

American College of Sports Medicine

added two episodes of strength

training a week, consisting of about

10 repetitions of 10 strengthening

exercises of all the major muscle groups.

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