Hydration and Exercise

Sweat Losses and Fluid Intake during Sports and Exercise

In any sporting event or exercise activity lasting longer than 30 minutes, there may be opportunities for (and advantages in) drinking fluids during the session to offset the fluid lost through sweat. The evaporation of sweat provides the major opportunity for the athlete to dissipate body heat produced as a by-product of muscular work or absorbed from a hot environment. Rates of sweat loss during exercise vary according to factors such as the intensity of exercise, environmental conditions (heat, humidity, airflow), and the athlete's size, clothing, and state of fitness/acclimatization. Typically, sweat rates vary across a range of sports or exercise activities from 0.5 to 2.0 L/h and can cause substantial losses of fluid and electrolytes.

The opportunities to consume fluids during sports or exercise activities vary according to the rules, environment, and culture, particularly during competitive situations. In sports, particularly team games and racket sports, there are breaks in play, such as substitutions, half-time, or changes of ends, in which competitors can grab a drink. However, in continuous events such as marathons, cycling races, and triathlon, the athlete must drink, literally, “on the road.” Access to fluids also determines intake and ranges from having to carry all supplies to being supported by trainers/handlers or having a network of aid stations during the race. Challenges include the need to slow down to obtain and consume the drink as well as the risk of gastrointestinal discomfort. Some degree of dehydration is inevitable in most sports because of the mismatch between the athlete's sweat losses and his or her capacity to replace fluids during the event. This is particularly the case in most highlevel sports, where high exercise intensities ensure high sweat rates and the athlete may be reluctant to sacrifice any time lost to drinking. Studies across a range of sports have reported that athletes [Page 588]typically drink at a rate that is around 50% to 70% of their sweat losses. A more recent phenomenon, however, is the observation that some athletes or exercisers actually drink more than they sweat; this will be discussed further later.

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