Drink up

Fluid replacement, otherwise known as hydration, is crucial for every individual regardless of the level of exercise activity. Losing as little as 2% of body mass due to dehydration can negatively affect a variety of physiological functions and lead to diminished performance capacity (Nieman, 1992).

The best time to hydrate the body is prior to exercise. All exercise routines, whether they be short duration, high power output exercise or prolonged moderately intense endurance activities, can be impaired when individuals begin with a fluid deficit (Sawka & Pandolf, 1990). Normal daily water intake should be two to three quarts (Berning, 1996). One hour before exercise, however, eight to 16 ounces of fluid are recommended, with eight to 12 ounces of fluid 10 to 15 minutes prior to the event. Hydrating one hour prior to activity will increase urine volume as much as four times the amount measured without pre-exercise fluid (McArdle et al, 1996). A pragmatic solution is 400 to 600 milliliters of water two hours before exercise to allow renal mechanisms sufficient time to regulate total body fluid volume.

The best time to replace lost fluid is during a given activity, although people typically drink insufficient volumes of fluid to offset sweat losses (McArdle et A 1996). In hot weather, it is common for individuals to dehydrate by two to six percent of their body weight during exercise despite the availability of adequate amounts of fluid (Noakes, 1993). The significance of this voluntary dehydration" must not be overlooked. The net result of electrolyte and water imbalance, associated with the failure to adequately replace fluids during exercise, is an increased rate of heat storage which can lead to disorders such as heat stroke (Sutton, 1990). Drinking one to two cups of fluid for every 15 to 20 minutes of exercise is a practical method for matching fluid ingestion with the rate of fluid loss due to sweating (Stopler-Kasdan, 1998).

Fluid replacement at the conclusion of exercise is also important. One particular strategy is to drink approximately two cups of fluid per pound of weight lost (Stopler-Kasdan, 1998). The choice of fluid replacement is not as crucial after exercise, providing the beverage is considered healthy and digestively tolerable. While fruit juice should be diluted 50/50 with water during exercise, straight apple juice may be fine afterward. Orange juice might also be a good choice after exercise. However, the acidity may be difficult for some people to tolerate on an empty stomach, as well as the reflux caused by the oil from the peel that gets into the juice (Gebo, 1998).

The negative impact of fluid deprivation on cardiovascular function and thermoregulation is well-established (McArdle et al, 1996). The current debate, however, concerns how specially designed sports drinks affect athletic performance. Water is an excellent source of hydration for exercise activity of less than one hour. During two to three hour events, consuming water alone shuts down the thirst mechanism at approximately 68% hydration and stimulates urine production (Covert Baily, 1997). Minerals in s (primarily sodium) prolong thirst, inhibit urine production and assist hydration to approximately 82%.

When exercising beyond one hour, rehydration should also include replenishing glycogen stores (Sicama, 1998). In the late stages of prolonged exercise, ingested carbohydrates become the main source of carbohydrate energy and can delay the onset of fatigue (Coyle and Montain, 1992). Additionally, the carbohydrates included in a fluid replacement solution can enhance intestinal absorption of water (Schedl et al, 1994). Most sports drinks on the market contain six to eight percent carbohydrate (Wilmore and Costill, 1994), usually in the form of glucose and sucrose, which are equally effective in delaying fatigue and improving performance (Saris et al, 1993). Performance is not improved when fructose is the predominant carbohydrate (Massicotte et al, 1989), and may in fact cause gastrointestinal distress (Murray et al, 1989).

It is important to drink, regardless of what you choose. The competitive nature of the sports drink companies tends to lead the consumer to believe their products are the best choice for rehydration. The reality, however, is that most of the products are similar and individual preference is still the key factor in making the right choice.

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