DOCTOR ON CALL/ASK THE EXPERT:MYSELF AND some friends like to shoot a few baskets for about half an hour after school. It's nothing serious, just a way of switching off before supervised study. Our PE teacher came up to us last week and said we should do some warm-ups before we start. We thought he was a bit over the top - it's not like we play competitively. What do you think?

WELL, FIRST off, its good to hear you are exercising regularly as a means of switching off. Any exercise, no matter how unstructured, is a great stress buster.

But you're right, we associate warming up and cooling down with structured team training. In some ways, wandering out to casually play soccer or basketball seems different and more relaxing because of this lack of formality.

At the same time, your PE teacher has probably seen how regular your sessions are. And it's likely you are more competitive than you think even if you're not formally counting scores.

So, does he have a point? The Scandinavians have done a lot of research into sports injuries. A 2005 study from the Norwegian University of Sport and Physical Education, published in the British Medical Journal, set out to investigate whether a structured warm-up programme helped to reduce the number of knee and ankle injuries in young sports people.

They recruited over 1,800 Olympic handball players aged 15 to 17 and split them into two groups. One half of the players were taught a warm-up programme designed to improve running and landing techniques as well as balance and strength. The control group were asked to carry on as normal for the eight-month season.

The researchers then measured the rate of injuries to the knee and ankle in the two groups. There were significantly fewer injuries in the group that followed the warm-up programme, with a 50 per cent reduction in acute knee and ankle injuries.

Warm-up exercises included the use of a wobble board and balance mat.

The particular emphasis was on developing stability through the "knee over toe" position. Each exercise took four to five minutes for a total warm-up time of 15 minutes.

By focusing on the alignment of the hip, knee and ankle, the intervention helped reduce the number of cruciate ligament and medical collateral ligament injuries to the knee.

The Norwegians concluded that the intervention would be useful in other sports like football, basketball and volleyball.

So it is something you may want to look at with your PE teacher. Given that you are limited to 30 minutes of play time, ask him if he could come up with a shorter, modified warm-up programme of five minutes or so.

Dr Muiris Houston is Medical Correspondent of The Irish Times. Email queries to sportsdoctor@irish-times.ie