This cooled blood then flows back to the body's core, thereby decreasing internal body temperature. The body cannot properly cool itself when dehydration occurs. Serious heat-related injuries or illnesses, such as heat exhaustion and heat stroke, can result when excessive fluid is lost and not replaced during exercise and the body temperature increases. Symptoms of heat exhaustion include dizziness, weakness, rapid pulse, low blood pressure, headache, and elevated body temperature. Symptoms of heat stroke can include sudden cessation of sweating, clumsiness or stumbling, disorientation, vomiting, and loss of consciousness.
Death can occur with heat stroke.
Dehydration reduces one's endurance and increases one's risk for heat-related illnesses, such as heat exhaustion and heat stroke. When the body becomes dehydrated, athletic performance can be greatly hindered. A water loss equal to 5 percent of body weight can reduce muscular work capacity by 20 to 30 percent. Table 1 shows the effects of dehydration on performance as measured by percent body weight lost as fluid during exercise. When You Lose Fluids During Exercise.