Health and sports experts claim a person can easily sweat off 3 liters of fluid per hour when exercising in hot, muggy weather. Without adequate replacement, dehydration can adversely affect the body's functioning. For example, without proper hydration the blood volume will decrease, forcing the heart to work harder to circulate nutrients. Less water means less glucose goes to working muscles, and less lactic acid is carried away. There is also less water to sweat off, and because sweating is how a body cools itself a dehydrated person will be hotter.