Hydration is a fundamental component to performance on any day, whether it be training or competition. There is a myriad of positives to being hydrated, when sufficiently hydrated your brain is more alert, your nerves send signals to your muscles quicker and your muscles contract with greater force. Not hydrating before, during and after exercise is one of the biggest mistakes you can make. The detriment in performance is well documented, often you will perceive exercise to be more difficult when dehydrated and because your muscles aren’t firing with as much force you will often be slower, particularly in endurance performance.
As a recommendation, you should consume 40ml per kilogram of bodyweight in a day (70kgx0.04=2.8litres), weigh yourself before and after exercise. If you have lost 1kg you should rehydrate 1L in addition to your daily minimum. From the example our 70kg man would drink 3.8 litres.