Too much exercise a worry in the long run

Forget the morning jog and go back to sleep: exercise may be bad for you.

Blame it on the free radicals, volatile little molecules in the body which are unleashed by exercise and have been implicated in a range of illnesses, from cardiovascular disease and cancer to accelerated ageing.

If there are too many free radicals roaming around, they can overwhelm anti-oxidants in the body (the good guys), leading to an imbalance called oxidative stress. But here's the difficulty: while science knows that exercise increases the production of free radicals, it has also shown that trained athletes are more resistant to oxidative stress.

So, to exercise or not to exercise? This is the question that Amanda Geraghty, a James Cook University PhD candidate in sports and exercise science, is attempting to answer. ''Both trained and untrained individuals have been shown to experience oxidative stress,'' she said. ''However, regular exercise has been shown to strengthen the resistance to this process.''

She hopes to be able to determine whether exercise can be tailored to reduce the risk of developing oxidative stress.

The key is to find out the impact of various exercises - high versus low intensity, short versus long sessions. Ms Geraghty is using ''healthy untrained males'' willing to hit an exercise bike for up to one hour and undergo blood tests to examine their levels of both free radicals and anti-oxidants.

She expects to take another 18 months to finish the research and submit her thesis, which could pinpoint the best kind of exercise regime to undertake.

And while the temptation may be to sit tight until the verdict is through, Ms Geraghty is blunt: ''I just want to emphasise I'm not saying that exercise is bad at all ... and I'm still encouraging people to exercise 30 minutes a day.''