A new research, published in Sports Medicine, says that dehydration may reduce strength by 2%, power by 3% and high-intensity endurance by 10% during exercising.
To avoid dehydration, the researchers recommend drinking near 250 ml of water 30 minutes before a workout to ensure the best function of your muscles, and then near 500 ml within 30 minutes after the finish.
How much to drink during the workout is more subjective, but Jo Scott-Dalgleish, a nutritional therapist, recommends up to 500 ml during a 1-hour workout.
After 90 minutes of a moderate workout, the number of glycogen stores in your body is reduced, and it’s time to start drinking electrolyte sports drinks.
Health experts warn that drinking too much water without replacing electrolytes is as bad as dehydration and may be even worse. It may cause hyponatremia, which leads to seizures, organ failure, and even death.
More information here.