Mariano Zabaleta rehydrates during his break

Matches on clay are particularly gruelling because of the length of rally, and a five-setter can easily last more than five hours.

The players' doctor, Dr Jacques Parier, told me that in these conditions, a player can lose more than seven litres in sweat over the course of a five-hour match.

It's a good way to lose weight in a hurry, although not really advisable, as each litre of water lost is the equivalent of a kilo in weight.

Obviously players have to prepare carefully and drink plenty of water, but, as Parier explained, it is not just water that they need.

Exposed flesh

It is important to drink enough, but not only water - they must take salt. When you sweat, you lose electrolytes and sodium.

And afterwards you must drink more and eat with salt.

If you have another match soon after, it is sometimes necessary to use a drip containing water, magnesium, sodium and potassium.

It is not doping - with a drip you can rehydrate in a short time.

But while the players know how to prepare well, the Paris public, it seems, do not.

Just walking around the grounds, the sun's toll is evident for all to see.

Much of the exposed flesh on display is as red as the famous Roland Garros clay.

Greg Rusedski feels the heat

Dr Daniel Boulanger, who treats the public, says the medical staff at Roland Garros have to deal with hundreds of patients every day, the vast majority of whom are casualties of the sun.

Fortunately for the spectators, however, some salvation is at hand.

There are a number of oases scattered around the grounds known as points fraicheurs.

The crowds flock like wildebeest to a watering hole.

Supplied by a well-known French mineral water company, the point fraicheur is like an outdoor shower, spraying out a fine mist of water that is cool, refreshing - and no doubt gently sparkling too.