http://www.healthstandnutrition.com/sports-nutrition-during-exercise Keeping well hydrated and fueled properly while participating in sports such as running, hiking, gym workouts can help you perform at your best. Here are some of the key things you need to know to train at your best: What are the signs of dehydration? Increased perceived effort (you ӦeelԠlike your workout is difficult). Difficulty with mental focus, concentration and balance. Increase in muscle cramps. Impaired aerobic exercise performance. May slow anaerobic power. What factors influence how much fluid you need for exercise? Individual differences in how much you sweat. The type of sport, duration, and intensity (the longer or more intense the exercise, the more you will sweat). Temperature of your environment (the hotter and more humid, the more you will sweat). Females generally have lower sweat rates than males. http://www.healthstandnutrition.com/sports-nutrition-during-exercise