Making up approximately 60 percent of the body, water helps maintain homeostasis by regulating core body temperature, helping blood pump freely, maintaining proper cell functioning, and assisting other physiological processes 1,2. When total body water (TBW) decreases in an amount greater than two percent of total body weight, a state of dehydration occurs, causing changes in physiological function that can lead to detriments in health and athletic performance 2,3. Maintaining euhydration (normal total body water level) is, therefore, essential to helping an athlete perform to their potential. While there is no one-size-fits-all recommendation to ensure an athlete is hydrated, monitoring hydration status and following an individualized hydration plan can help athletes reach their ideal hydration state.
The goal for an athlete is to be euhydrated before, during and after exercise to prevent performance-related decrements due to water loss. Unfortunately, many athletes start practice or competition hypohydrated (decreased TBW), and any attempt to “catch up” is often unsuccessful. Total body water levels vary and are based on age, gender, race, and, mostly, lean muscle mass (fat-free mass is 70 percent to 80 percent water) 1. At the critical two percent point (a mere four-pound water weight loss in a 195 pound athlete), detrimental physiological effects begin, and include an increase in core temperature and heart rate, plus alterations in metabolic and central nervous system function 2. As a result of these changes, aerobic performance is adversely affected; the degree to which is dependent on factors such as type of activity, environmental conditions, heat acclimatization and athletic ability 2. Cognitive and mental performance alterations are particularly important in situations where concentration, skilled tasks and tactical issues are involved (e.g. in all sports, at all times). Dehydration puts the athlete at risk for heat exhaustion and heat stroke due to reduced cardiac stability, altered intracranial volume and reduced cerebral blood flow responses 2. Additionally, dehydration and decreased electrolytes can increase the tendency for cramping, and can escalate the consequences of rhabdomyolysis (release of damaged muscle cells into the bloodstream) 2,3.
The general recommended daily fluid intake is approximately 91 oz for female adults and 125 oz for males (with roughly 20 percent of that coming from food intake) 1. Athletes, however, have a higher need based on their increased activity levels. When developing a hydration plan for athletes, hydration status should first be assessed and recommendations should follow individualized needs.
Multiple measures of hydration exist, but practicality is a major factor guiding use. Urine color and body weight can be easily measured and provide valuable information for the hydration plan. Urine that is a pale, lemonade color indicates a hydrated state, while a darker, apple-juice color indicates a dehydrated state (click for the Assessing Hydration Fact Sheet).
Morning body weight under normal conditions after initial void should be used as a baseline, hydrated weight. Fluid intake during exercise should be the focus of the hydration plan when there is adequate food or drink consumption and proper recovery time between competitions or practice sessions. In situations where there is reduced recovery time (two-a-days, multi-event tournaments), reduced consumption (weight-controlled sports, lack of food/drink availability, extreme temperatures), or altered fluid loss (increased duration/intensity of exercise, altered temperatures, electrolyte imbalances), dehydration is more likely and the hydration plan should emphasize hydration before, during, and after exercise.
During exercise, athletes lose water via the release of sweat as a compensatory mechanism for regulating the heat produced from activity. Individual sweat rates vary and depend on weight, genetics, environment, heat acclimatization, exercise intensity and duration as well as other factors. Higher sweat rates occur with male athletes, large athletes and athletes with an increased core temperature (e.g. from an acute illness).
Weighing an athlete before and after exercise (multiple times and under various conditions) can approximate the amount of sweat lost and offer a starting point for how much fluid consumption is necessary during exercise to prevent dehydration 2,3 For events lasting less than an hour, water is adequate for maintaining hydration. For longer events (and in the case of “salty sweaters”), a sports drink of no more than eight percent carbohydrate should be the fluid of choice to ensure fluid absorption and to maintain electrolyte balance.
Before activity or competition, the athlete should slowly drink five to seven mililiters of water per kilogram of body weight four hours before the event to help promote euhydration 2,3. If euhydration is not achieved, another three to five milliliters per kilogram should be consumed two hours before the event 2. As previously described, athletes should determine their individual sweat rate so that necessary measures can be taken to prevent dehydration during activity. If the athlete does become dehydrated, normal fluid and food consumption after activity should return the athlete to a hydrated state. Incorporating high water content foods, such as broth soups, fruit, and vegetables, will facilitate regaining hydration status. If rapid rehydration is necessary, 16 to 24 ounces of fluid should be consumed for every pound lost (the extra volume accounts for water losses that accompany rapid consumption of large fluid volumes) 2,3. Sports drinks are quite beneficial in these situations because they help to rebalance electrolytes, increase the amount of fluid ingested and enhance fluid absorption.
Just like training and proper fueling, maintaining hydration is an essential part of an athlete’s performance plan. In general, athletes know they need to hydrate during activity, but truly personalizing the recommendations for what, when and how much to drink is key for success.
This article was written for the Sport Science Institute by SCAN Registered Dietitians (RDs). For advice on customizing a hydration plan, consult an RD who specializes in sports, particularly a Board Certified Specialist in Sports Dietetics (CSSD). Find a SCAN RD at www.scandpg.org.
Last Updated: Aug 8, 2013