By Priya Suri

Too much of a good thing can turn out to be bad - even when it's something as beneficial as exercise.

Most people struggle to fit regular exercise into their daily routine but a few become obsessed with working out and even exercise when ill or in bad weather.

Since each person is born with his own natural stamina level, it's difficult to define how much exercise can be considered excessive.

Dr Jason Chia, consultant sports physician at Changi Sports Medicine Centre, said one of the repercussions of excessive exercise is overuse injuries - damage to tendons, bones, muscles and joints from repetitive strain.

Once injured, the exercise addict might decide to continue exercising by ignoring pain signals or denying that they exist.

When he does not get enough rest or let injuries heal, his physical activity will actually decrease his performance instead of improving it, said DrChia. Fitness junkies may also injure themselves by falling victim to what Dr Chia calls the 'too much, too soon' syndrome.

This means that they attempt to do too much in a short time, either by fitting in too many training sessions per week or by increasing the intensity of exercise to a level their body can't handle.

Personal trainer Alvin Cheah from Planet Fitness has seen this phenomenon with some new gym members who are very enthusiastic and may try to do too much at the start. These novices want quick results and attempt things their bodies may not be ready for.

People who are addicted to exercise have different motivations for pushing themselves to the limit.

Though they may start off enjoying occasional exercise, they gradually become addicted to the 'high' or 'buzz' they feel after a long workout.

Dr Tan Jee Lim, consultant orthopaedic sports surgeon at Gleneagles Medical Centre, said that this is due to the release of endorphins that are produced during strenuous workouts. The so-called 'runner's high' is attributed to this euphoria-producing chemical.

Others may compulsively exercise because they are afraid of gaining weight. These people may have an accompanying eating disorder such as bulimia or anorexia.

Dr Tan said that women who exercise excessively and do not receive the proper nutrients from food may disrupt the balance of hormones in their bodies, causing a change in the menstrual cycle.

Some may even stop getting monthly periods, a sign that their oestrogen levels have dropped. Since oestrogen is needed to regulate bone metabolism, this may put them at greater risk of developing osteoporosis, a disease in which bones become brittle.

For men, over-exercising can affect their fertility. Dr Tan said that it is well documented that the decrease in sperm density and activity can be linked to excessive exercise in sports such as cycling.

Both men and women can experience temporary suppression of their immune systems during bouts of over-exercise. This means that he or she would be more susceptible to infection.

Although excessive exercise may not be a common problem here, doctors say they have seen an increase in people of all age groups who are exercising regularly.

In fact, the 2004 National Health Survey found that the proportion of adults aged 18 to 64 who exercise regularly (three or more times a week for at least 20 minutes each time) rose by more than 8per cent from 1998.

While this is a positive trend, doctors advise those who have been sedentary for some time to seek medical advice before embarking on a vigorous exercise programme.

Dr Tan advises: 'A good rule of thumb is to increase activity by 10 per cent every week. For example, you can increase your running distance by 10 per cent or your speed by 10 per cent. But not both.'

psuri@sph.com.sg

The 2004 National Health Survey found that the proportion of adults aged 18 to 64 who exercise regularly rose by more than 8% from 1998.

This story was first published in Mind Your Body, The Straits Times, on July 2, 2008.