Water is vital to life and performance. Total body mass is 60% water. Muscle mass is 75% water. Blood is 90% water. As the body becomes dehydrated, various body functions are affected. Both body and blood fluid volume decreases. As the circulating blood volume decreases, there is less nutrient-rich, oxygen- containing blood delivered to the brain and working muscles. This poor circulation can impact muscle function as well as perceived exertion. With a decreased blood volume, the heart has to work harder by increasing heart rate. Since sweat is 99% water, the ability of the body to cool itself becomes more difficult, and core body temperature rises as the body’s fluid stores become depleted. This in turn increases the risk for suboptimal performance, heat illness, heatstroke, injury and delayed recovery. Research indicates that many athletes perform in a mild state of dehydration. During training, even when fluid is readily available, athletes tend to replace only 50% of the fluid lost as sweat. It is not uncommon to lose 32-64 ounces of sweat while exercising.

The more dehydrated an athlete becomes, the greater the potential for gastrointestinal distress due to delayed stomach emptying. It has been suggested that many athletes can tolerate up to a 2% loss of fluid with minimal impact on performance. As the percentage of body weight loss exceeds 2%, an athlete can expect perceived exertion to increase and overall training pace to slow.


Early warning signs of dehydration include thirst, fatigue, loss of appetite, nausea, dizziness and flushed skin. As the severity of dehydration increases, signs may include headache, muscle cramping, heat intolerance, stumbling and clumsiness.

Daily Fluid Needs

Fluid intake to meet base daily needs (in ounces) is approximately half of the athlete’s body weight (in pounds). Water, juices, fruit drinks, sports drinks, milk and tea may be acceptable fluid sources. Both alcoholic and caffeinated beverages should be minimized as they may have a slightly diuretic effect (one loses more fluid via the urine). The best indicator of adequate daily hydration is frequent trips to the restroom (every 2-3 hours), producing a pale to near colorless urine of sufficient volume. If the urine looks like apple juice, it is an indication that more fluid should be consumed. Food choices can also contribute to an athlete’s fluid needs for the day. A diet that contains ample amount of high water-containing fruits and vegetables (nine or more servings per day) can provide up to 30% of daily fluid needs. Maintaining adequate hydration is paramount to overall well being and physical performance. Table 6.4 can assist in advising athletes of their hydration plan.

CAUTION: Athletes can drink too much. Hyponatremia, also known as low blood sodium, can be a serious health consequence of drinking too much water or other low sodium liquids for a prolonged period of time. Signs and symptoms include nausea and vomiting, headaches, puffiness, disorientation and confusion. Athletes can estimate their fluid loss by calculating sweat rate.