At the 2018 Australian Open, players walked off court dizzy and cramping in 40°C heat, a few after losing close to 4 liters of sweat in one match. Tennis hides how hard it is on the body. A singles match can run 2 to 5 hours in direct sun, with no clock to end it and only 90 seconds at each changeover to recover. A player who treats hydration as an afterthought loses the third set to his own body long before his opponent earns it. Good hydration starts hours before the warm-up and continues past the final point.

The Hydration Demands of Tennis

Tennis is among the most dehydrating sports because the work never fully stops. In warm conditions a player loses 1 to 2.5 liters of sweat per hour, and elite players in heat and humidity can reach 3 to 5 liters per hour. Each liter of sweat takes 1,000 to 1,500 milligrams of sodium with it, and that figure varies up to 15 times from one player to the next. That variation is why a one-size drink fails some players, dousing one in salt he does not need and leaving another far short.

The margin for error is thin. A water deficit of only 1% to 2% of body weight measurably slows footwork, lengthens reaction time, and dulls shot selection. In a five-set match, a player who falls behind on fluid in the first hour rarely catches up, because the body cannot absorb as fast as it sweats in the heat. Acclimation helps but does not erase the problem. A heat-adapted player sweats earlier and more, which cools better and pulls even more fluid out per hour.

Before the First Serve

The match is half-decided before the first serve. A player who starts even slightly dehydrated has no runway to recover once the points begin. The standard pre-match approach is 500 to 700 milliliters of fluid in the 2 hours before play, then another 200 to 300 milliliters about 15 minutes before walking on. A salty snack a few hours out helps a player walk on already topped up.

Sodium belongs in that pre-match fluid too. A pinch of salt or an electrolyte mix helps the body keep the water it takes in and nudges thirst so a player keeps sipping. Walking on court fully topped up buys 20 to 30 minutes of margin before sweat losses start to bite.

The Match-Day Drink

The drink a player brings onto the court decides how the second hour compares to the first. Water alone replaces the volume while leaving the sodium losses untouched, which is why most players courtside reach for something with salt in it. A measured electrolyte powder for hydration stirred into a bottle lets a player match the sodium and carbohydrate to how heavily they sweat, a precision a generic sports drink cannot offer.

The target is straightforward. Enough sodium to keep the fluid in and a volume the stomach can take during a 90-second changeover, with a little carbohydrate for energy and faster absorption.

Drinking Through the Heat

During the match, the changeover is the only window to drink, and 90 seconds is not long. In mild conditions, around 200 milliliters of an electrolyte fluid each changeover keeps a player even. Above 27°C, a heavy sweater needs closer to 400 milliliters every changeover, roughly every 15 minutes of play. When the Australian Open enforces its extreme heat policy, play stops and roofs close once the on-court stress scale reaches a set point.

The trend is getting worse. Grand Slam events now see record-breaking temperatures that turn a routine match into a medical risk, and a player’s drinking has to increase as the temperature rises. The hotter it gets, the more sodium leaves in sweat, and the more a plain-water plan falls short. A cold drink helps too, pulling a little core heat out as it goes down.

Heat Cramps and Sodium

A cramp rarely comes out of nowhere. When a player seizes up late in a match in the heat, the usual cause is a sodium deficit built across that match and the matches before it. The muscles worked hardest, calves, forearms, the core, lock first. Two players side by side can lose very different amounts of salt, so a cramp-prone player has to learn his own number.

The fix is sodium and fluid together, taken early enough to matter. Research on muscle cramps points to salt and neuromuscular reflex triggers as the bigger factors, which is why courtside kits often hold salt tablets and pickle juice alongside the water. A player prone to cramps has to front-load sodium before he feels the first twitch, because once a cramp hits mid-point, the match is usually already slipping.

After the Last Point

Recovery starts the moment the handshake ends. A player is more dehydrated than he feels for 2 to 4 hours after a hard match, still down fluid that thirst no longer flags. The standard target is to drink about 150% of the fluid lost, since a third of it leaves again as urine.

Sodium and a carbohydrate-and-protein snack within 30 minutes speed the refill and start muscle repair. Low-fat chocolate milk is a common recovery choice, refilling muscle fuel while the sodium pulls water back into circulation. Skipping this step is how a player shows up flat for the next round in a tournament. Dehydration that lingers for hours carries real risk. Across back-to-back match days, it becomes a health threat, from heat illness to kidney strain.

A Plan for the Whole Match

The players who cramped out in Melbourne lost to their own fluid math as much as to an opponent. By the time it mattered, they were too far behind on water and sodium to recover. Hydration in tennis spans the whole match. It starts hours before warm-up and continues well past the last point.

Get the inputs right and the body stops being the opponent. A player who drinks to his own sweat rate, salts the fluid, and starts early keeps the one edge a long match rewards most, a body that performs as well in the fifth set as in the first.