Why a stroll round the block is better than running a marathon

HOW’S that new Year’s resolution to get super-fit going? If you’ve already shoved your expensive trainers — along with your marathon-running aspirations — to the back of a cupboard, don’t feel too guilty.

Although a study out today has found that occasionally getting out of breath is good for you, a host of other research suggests you can have too much of a good thing. For it seems you’re better off taking a brisk walk that leaves you out of puff, or a gentle jog around the block, than training for a marathon.

Studies have shown that extreme regimens can expose committed fitness-seekers to memory problems, tooth loss, failing sex drive and fertility, muscle wastage, poor immunity to infection and even a lifetime of heart trouble. They are also prone to injury.

Steve Berkman, a physiotherapist from London, reports a big rise in the number of women undertaking challenges such as the London Marathon and triathlons.

‘Only this morning I have had three female first-time marathon runners in the clinic,’ he says. ‘They may have the cardiovascular fitness to run 15 to 20 miles at the weekend, but in the rush to get fit they haven’t given their muscles and tendons time to adapt, so they got injured.’

The contrast between gentle and rigorous regimens was highlighted this year by Danish investigators who tracked more than 5,000 people over a 12-year period.

They found that light joggers — who ran no more than three times a week and for no more than two and a half hours in total — had the lowest rates of death in the group, compared both with those who did no exercise at all and with the most extreme exercisers.

A nine-year Oxford University study of more than a million middleaged British women, published in February in the journal Circulation, found that those who did gentle exercise such as walking, gardening or cycling, four times a week were 20 per cent less likely to suffer from heart problems, stroke and blood clots than inactive women.

However, the researchers also found that women who did daily strenuous activity were at increased risk of heart disease and stroke.

Oneexplanation for this seesaw between benefit and risk is that moderate exercise can increase the length of people’s telomeres. These are protective caps of DnA and proteins that sit at the end of our chromosomes, helping them remain stable.

As telomeres shorten, they start to fall apart, causing our cells to age and die more quickly. Shorter telomeres are associated with an increased risk of premature death and with age-related diseases, including many cancers.

In 2013, a study published in the Lancet found that moderate exercise produced a healthy stimulus that helped to promote the growth of telomeres when combined with a healthy diet.

The Danish study, however, suggests extremely strenuous exercise has the opposite effect, causing telomeres to shorten.

Lead researcher Dr Peter Schnohr, a cardiologist with the Copenhagen City Heart Study, says: ‘If your goal is to improve life expectancy, jogging a few times a week at a moderate pace is a good strategy. Anything more may be harmful.’

This contrast in benefit and risk between light and strenuous exercise has also been highlighted by recent studies on the brain. In november, Japanese scientists reported how two weeks of low-intensity exercise such as brisk walking boosts activity in the hippocampus, a brain region important for forming new memories.

However, intense exercise appears to provide no such benefits, say the biochemists in the International Journal of Sports Medicine.

A separate Chinese study shows that exercising to the point of exhaustion may cause chemical imbalances that kill brain cells in the hippocampus and reduce surviving cells’ ability to communicate with each other.

Too much exercise seems to cause an overload of the brain chemical glutamate, which may cause clinical problems with memory and thinking in athletes.

Tooth loss may also be a concern. A 2013 investigation in the British Journal of Sports Medicine examining 278 athletes during the 2012 Olympics found that most had high levels of tooth decay, tooth loss and gum disease.

And in September, a team of German dentists claimed to have discovered why. Lead researcher Dr Cornelia Frese says our saliva changes when we exercise hard. People who run fast for more than 35 minutes see their spit become much dryer and then more alkaline, she says.

Saliva ‘ has a very protective function’ for teeth, so reducing it threatens dental health. Furthermore, alkaline saliva allows tooth-rotting plaques of bacteria to grow on the enamel, Dr Frese reports in the Scandinavian Journal of Medicine & Science in Sports.

And, as research shows, toothdecay bacteria are associated with an increased risk of heart attack and dementia, although the reason for this is unclear.

Strenuous exercise regimens can also interfere with a woman’s monthly cycle. exercise-induced amenorrhea ( the absence of menstruation) is a common, reversible condition that afflicts up to a quarter of female athletes. Frequent intense exercise stresses women’s bodies in such a way as to interrupt the normal release of a chemical called gonadotropin-releasing hormone, which prompts the release of eggs. This can mean periods stopping or becoming less regular.

Men’s sex drive can also diminish due to heavy exercise.

Australian researchers, meanwhile, have added another drawback — increased susceptibility to infections. The Queensland University investigators found that strain on the body from intense exercise can cause a drop in the blood levels of infection-fighting T-cells.

But the most worrying threat, as numerous studies have shown, is heart damage.

Like any other muscle, the heart can enlarge with regular exercise. Vigorous sustained exercise can particularly affect the right ventricle (the lower right-hand chamber), according to a study last year in the journal Pulmonary Circulation.

The researchers explained that an enlarged right ventricle can alter the heart’s electrical system, causing abnormalities in rhythm that can result in lifelong problems with chest pain, breathlessness or fainting.

These heart problems can even be fatal — one recreational runner in 15,000 suffers sudden cardiac death each year.

GIVenthese risks, one has to ask if extreme exercise is worth it.

Anthony D’Silva, a cardiovascular science clinical research fellow at St George’s, University of London, wrote a review of sudden cardiac death in the journal The Physician and Sports Medicine. He says: ‘ evidence suggests that beyond an optimal level of fitness, the principle of diminishing returns applies. exercise appears to most benefit people who are least active.’

Dr Miranda Armstrong, who conducted the new Oxford University study, found that women who prefer to exercise vigorously can enjoy the same benefits as those who exercise gently four times a week, if they do only ten minutes’ vigorous exercise twice a week.

It’s a prescription we can all take on board. ‘Moderation in all things’ has once again been shown to be the wisest option.