IT'S been a difficult fortnight for some of the world's leading tennis players in Melbourne. The Australian Open usually throws up a few surprises as the major stars search for form so early in the season. Over the past 12 days, though, simply staying on their feet in the heat has caused a few players considerable difficulty while, for the likes of Boris Becker and Steffi Graf, producing quality tennis as well has simply proven to be too much.

Becker was the first of the major stars to fall victim to the conditions with the former world number one complaining that "all I had left was my serve" after being beaten in a gruelling contest by Carlos Moya.

It was Graf's defeat, however (her first Grand Slam loss in 46 matches) at the hands of South Africa's Amanda Coetzer that gave a clearer indication of the extent of the problem being experienced by competitors. The world number one was clearly unable to cope with temperatures of around 50C (120).

The point was reinforced when Goran Ivanisevic wandered off court in a daze from this three hour encounter with Christian Ruud and admitted that through the latter stages of the match - I didn't feel too much in my legs. I was out of it, I didn't know where I was.

That the Croatian, like everybody else, had made it through the match with any more serious problems is, in fact, a tribute to the remarkable ability of professional athletes to cope with the sort of extreme heat that has become an increasingly regular feature of sport these days.

Special clothing has been developed to help the body cool itself through sweating and a great deal of work is done by the leading players to prepare for these sort of conditions but the sort of temperatures recorded at Melbourne Park over the past two weeks (it reached 60C at one point) are still considered to be at the very upper limits of what any sports person can cope with.

In fact, a person's core body temperature going above 45C would pose a serious threat of death with brain damage a possibility at a couple of degrees below that. To help prevent this a person's body will attempt to reduce the problem by pumping more blood to the skin where it can be cooled (blood flow to the fingers, for example, can increase 90-fold) but this, in turn, can leave less blood for the brain which becomes starved of oxygen.

"Drinking is the main thing," says Dr Geraldine Barniville of the Human Performance Laboratory in Trinity College. "If they didn't take fluids regularly in those sort of conditions, basically they'd be dead."

Also of vital importance is she player's clothing, with light white sportswear cutting the amount of heat absorbed from the sun by up to half. The use of a material that allows the player's sweat to escape is also highly beneficial for the evaporation of these body fluids is often the only method by which the body can successfully cool itself in very hot conditions - even this can be greatly hindered in more humid environments such as Las Vegas, Orlando and Atlanta where the likes of Barry McGuigan, Stephen Staunton and Sonia O'Sullivan have all suffered in recent years.

A third factor is air flow with any breeze at all helping to cool body temperatures. Heat loss is, in fact, proportional to the square of wind speed so if the latter doubles the former is increased by four times but this has become increasingly irrelevant in modern sports stadiums, particularly in tennis, where there is little or no air movement over the playing surface.

The upshot is that, even after going to considerable trouble to limit the risks many players must receive considerable amounts of liquid intravenously after coming off court with Pete Sampras receiving four pints of water in this way after one match in last year's US Open - a figure which Dr Barniville considers to be surprisingly low in the circumstances.

"This sort of thing, where people have to be rehydrated, would be common place after marathons and cycling events and in many cases there would be a medical centre near the finish line to cope with the need," she says.

Players lower down the earnings ladder have less access to professional medical advice and little opportunity for acclimatisation as Irish professional Owen Casey can testify.

"I've had virtually no training in this, it's all been trial and error. You get used to looking after yourself but sometimes, when they put you on at noon in somewhere extremely hot, it's almost impossible.

"It's a very fine balance between taking too little fluid and dehydrating and taking too much so that you can hardly play," he says before citing the example of a match he played in the Philippines in 1995 when, at 4-4 in the deciding set he had to concede the match due to severe cramps caused by lack of fluids.

Last Monday Sampras, after winning in even hotter conditions than Graf had had to play in, said that it was only a matter of time before the death of a player caused the abandonment of mid-afternoon matches at the hotter venues. This view was supported by Gerald Segal of the Australian Medical Association while others have expressed concern for the safety of spectators at some events.