Gym won't fix it

Helen Foster warns of the perils of keep-fit excesses

The exercise season is upon us, January being the busiest time of the year at any gym as old members work off the excesses of Christmas and new ones the excesses of the past five years. But experts warn that we should proceed with care: throwing yourself too vigorously into a new fitness regime can make you vulnerable to a number of health risks, including osteoporosis and reduced fertility.

'Exercise is a stress on the body,' says Dr Nick Webborn, medical advisor to the National Sports Medicine Institute. 'That's how it makes you fitter. You stimulate your body and it adapts to this stimulus by building muscle and strengthening the heart and lungs.' Done correctly, this will be one of the most potent things you can do for your health - moderate exercise has been shown to lower the risk of heart disease, some cancers and endless day-to-day ailments. Increasingly, however, research is demonstrating how many of our workout habits mean that the health benefits of regular exercise are being overridden by the negative effects - that is, by attempting to be too fit too fast, we don't strengthen our body through exercise, we actually attack it.

Problems occur for one of three reasons: we either work out too hard, for too long or too often. Of these, experts believe working too hard is the most damaging. If you work out really hard, all the ways in which your body is supposed to adapt to exercise stress go out of control. Take your immune system - ideally, exercise should stress it into producing more fighting cells, but if you work too hard this doesn't happen. Instead, it stresses it so much that the vital killer cells that are supposed to protect us are actually destroyed and for up to 24 hours any bug in the vicinity can take hold (one reason a third of marathon runners get sick after the race).

Outside of the immune system, you'll find that instead of reducing the effects of stress on the body, a high-intensity workout actually increases levels of the most harmful stress hormone, cortisol, causing endless problems for circulation and the nervous system. And while moderate exercise causes your bones to go into a process of recycling - during a normal workout, they are broken down by cells called osteoclasts ready to be mended by so-called osteoblasts afterwards - working out too hard knocks this process out of balance and the amount of bone broken down is increased. Add to this the fact that heavy exercise can cut oestrogen levels in the body, and it's easy to see why new research shows increasing numbers of athletes getting osteoporosis up to 20 years earlier than normal.

Another effect of overdoing exercise, is the overproduction of molecules called free radicals which rampage around the body attacking healthy cells. At moderate exercise levels, free radical increase can be fought by your body, but during an intense workout some areas of the body produce as much as 200 times more free radicals than normal, increasing free-radical damage to cells - a process which has been linked to everything from cataracts to cancer.

Preventing these problems is relatively easy. You monitor the intensity of your workout and so prevent yourself from working out too hard. 'The idea is to ensure that the majority of your workout is done at around 70 per cent of your maximum heart rate,' says Dr Ian Swaine, principal lecturer in exercise physiology at De Montfort University. 'You work this out by subtracting your age away from 220, then working out 70 per cent of this. This is the number of beats per minute your heart should beat, and it's the level at which you should exercise to maximise the gains made from exercise and minimise the negatives.'

This doesn't mean, however, that as long as you keep working out steadily, you can spend hour after hour in the gym. Working out for too long or too many times in a week can also cause problems. Ralph Pffanberg Jr and his team at Stanford University Medical School studied nearly 17,000 men and found that exercisers who burnt between 2,000 and 3,000 calories a week exercising (about three-and-a-half to five hours of moderate running or cycling) had significantly lower death rates from heart disease than non-exercisers. However, when men burnt more than 3,000 calories a week (about four 75-minute sessions), this protective effect began to decline and death rates started to climb again. Similar thresholds have been shown for women. The sensible exerciser, therefore, will aim for the 2,000 to 3,000 calorie mark - about about three-and- a-half to five hours a week, with no session lasting longer than one hour.

You should also make sure you rest for a day between sessions. 'Many people think this will lower your fitness level, but that's not true. The gains you make when you work out actually occur in the rest period for 24 hours afterward as your body repairs. It can't do this if you're working out again,' says Professor Mike Gleeson from the School of Exercise Science at the University of Birmingham. If you insist on training every day, Gleeson says, 'you should at least ensure a heavy workout is followed by a light day using different muscle groups.'

Of course, if you are training for an endurance event like a marathon, cutting back won't be an option. In this case, your protection comes from your diet. What you do or don't eat can make a huge difference to the effects that exercise can have. Start by supplementing with the antioxidant nutrients that will help fight free-radical damage. Studies at Washington University School of Medicine showed that exercisers given 600iu of vitamin E, 1,000mg of vitamin C and 30mg of beta carotene before they worked out produced 36 per cent fewer free radicals during their workout than normal. 'You can also cut immuno-suppression by ensuring you eat before a workout,' says Professor Gleeson. 'The immune system gets more depressed when people work out on an empty stomach.' He also points out that exercising in extremes of temperature increases the risk of immuno-suppression.

Finally, watch your equipment - if it's not up to scratch, you might find that it's not just your immune system you have to worry about. A recent Austrian study showed that 95 per cent of men who mountain-biked about 3,000 miles a year had developed deformities in the scrotum that could lead to fertility problems in the future. It was believed much of the problems were caused by knocks to the testes from bikes with suspension problems and hard saddles. This echoed findings that showed that high-duration cyclists were developing impotency due to damage to the nerve endings in the groin caused through crotch-to-saddle contact.

Of more universal concern is the increase in risk of injury to the the knees and back caused by wearing trainers that have lost their suspension. Make sure you replace training shoes every 500 miles of running, or about every 100 hours of any other exercise. If you aren't sure how many miles your footwear has logged, take them to a sports shop, try one new trainer and one old trainer at the same time and run, jump, walk - whatever - just concentrate on how your body feels as it hits the ground. If the new shoe feels dramatically bouncier, you need to buy new shoes.

Overall, what's important is to listen to your body and to aim to strengthen and improve it through sensible exercise. Doing so will bring many benefits, ranging from protecting your heart to creating better orgasms.

It's also worth bearing in mind that, according to Ian Swaine, 'the benefits of exercise are so powerful that even if you are working too hard you have less risk of major health problems than a couch potato. But for optimum gain, get the balance right.'

Take a break: work out too hard and you'll pay the price

Experts recommend that you look out for the following signs - if you are experiencing more than two or three of them then it's time to take a rest .

 Your resting heart rate is 8bpm more than normal. Regular exercisers should get used to knowing their heart rate by taking it first thing in the morning (while still in bed). If it increases by more than 8bpm over a day, your body is trying to tell you something - it could be that you're coming down with a bug, it could be that you're overdoing it. Either way, you need a rest.

 Has your workout got harder? If you're finding it significantly harder to do your normal programme, take it a bit easier.

 How are your POMS? The effects of exercise are not just physical. When looking for overtraining, experts measure something called the Profile of Mood States (POMs). If you find you're getting more depressed, having more mood swings, feeling irritable or experiencing loss of libido, take a break.

 Are you fatigued or having trouble sleeping? Both can be signs of overtraining.

 How's your health? Frequent infections (particularly respiratory infections) are a sign that your immune system is suppressed, which is a sign that you're working too hard. Be sure to take a break and include proper rest periods.