When the World Cup kicks-off in a few hours it'll be interesting to see how the footballers cope with the temperature and humidity of Brazil. Obviously, the players from the host nation Brazil are in a prime position to stay on top of things, but how will some of the other nations, such as England, deal with the heat and hydration? England's first game is on Saturday against Italy in Manaus, where temperatures are expected to reach 32C with humidity at 80 per cent. At the World Cup in Mexico in 1970 the players had to cope with similar conditions to those in Brazil, according to the then captain Alan Mullery. He told Sky Sports News: "It was extremely difficult after games when you were full of aches and pains because you were dehydrated, because we weren_t allowed bottles of water in those days, in the matches." Hydration is a measure of how much water there is in the body; and for footballers, drinking too little or losing too much water through sweating will have a negative effect on their performance. They won't be as fast at running, or be able to cover as much distance and their overall reactions will be generally slower. Hydration occurs because exercise increases the heat in the body, and sweating helps you to lose this heat, keeping you cool and preventing you from overheating. But if you're not replacing this sweat with water or other drinks then you'll continue to overheat, and at the extreme you could suffer heat stress. Thirst is a poor indicator of hydration status, since you are already dehydrated by the time the thirst mechanism kicks in. One of the best things you can do if training or taking part in sport is to drink at least 500ml of water one hour before you start; then have a 200ml glass 15 to 20 minutes before you start. It's recommended that you drink approximately 200ml of fluid every 15 to 20 minutes during training. Naturally, in hot weather _ such as that in Brazil _ you may need to drink more than this, and less in cold weather if you're not sweating and the session isn't that intense. One way to tell if you are adequately replacing sweat losses is to check the colour and quantity of your urine. If it is very dark you need to drink more fluids; if it's pale yellow your body has returned to its normal water balance. You can also monitor your sweat loss by weighing yourself before and after training and playing sport. For every 1kg of weight that you lose, you should drink 1500ml of fluid. Importantly though you should monitor how you actually feel; if you're chronically fatigued, have a headache, or feel lethargic then you may be acutely dehydrated and you should continue to drink until you start to feel better. Sport has developed a lot since Mexico 1970; it's become a science so the World Cup squads will be prepared for whatever the weather in Brazil throws at them, thanks to their medical teams. Roll on Saturday night; England v Italy!