# Drinking for Sport Performance

September 15, 2012 | Erik Sesbreno

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Good hydration is critical for optimizing health and sport performance. Although athletes acknowledge the importance of proper fueling, deciding how much liquid is needed during exercise and competition can be confusing.

Undoubtedly, water plays an important role in sport performance. For example, water in blood transports glucose, oxygen and fats to working muscles. It can also carry metabolic waste such as carbon dioxide and lactic acid. This process removes impurities from the body by eliminating waste product through urine.

To make sure athletes are consistently performing at their best, it's important to be aware of factors that can influence fluid requirements. Water is lost through sweat. The losses are determined primarily by the intensity and duration of the exercise, as well as by ambient temperature and humidity. A reduction in fluid volume affects blood flow to the skin, allowing body temperature to rise.

Dehydration compromises high-intensity and endurance workouts by reducing power output and impairing mental concentration. Fluid loss of five percent reportedly can decrease the capacity to work by 30 percent. To prevent this from happening, it's important to test your rate of fluid loss during training and competition.

There's an easy way to test fluid loss during physical activity. All you need is a calculator and a weight scale. The first step is weigh yourself approximately 15 to 30 minutes before exercise and after drinking. Then after practice and after drying yourself off, record your weight again in the same amount of clothing as before. Convert to kilograms by dividing your weight in pounds by 2.2. It's easier to estimate your fluid loss when your weight is in kilograms, because one kg of body weight equals one liter of fluid.

Now complete the following calculation: divide the number of kg lost during your workout by your pre-workout weight. Example: a 176-pound athlete weighs 80 kg. If he loses two kgs during his workout, the calculation is: -2/80 = -.025. Multiply the resulting number by 100 to get your percentage of fluid loss (-2.5% in the preceding example). If the result is a negative value, you lost fluid. If your number is greater than two percent, you lost too much fluid and likely experienced a decline in physical performance. At this level of dehydration, it is sometimes difficult subjectively to identify a decline in performance. It's often imperceptible to athletes unless they're severely dehydrated. During intense exercise, three hours or more, athletes may tolerate a loss of weight slightly above two percent because of changes unrelated to sweat loss. Therefore, in general, it's important to limit fluid loss to within one to two percent of your initial body weight.

It's equally important to avoid overdrinking to a point where your post-exercise weight is greater than your pre-weight. Overhydration can lead to headache and disorientation, and, in serious cases, coma or death. Overdrinking is more likely to occur when exercise is performed in a cool environment and at low intensity.

Photo: Eastbayri.com

- Erik Sesbreno is a sport dietitian registered with the College of Dietitians of Ontario. As a provincial executive member of the Dietitians of Canada's Sport...
- Erik Sesbreno is a sport dietitian registered with the College of Dietitians of Ontario. As a provincial executive member of the Dietitians of Canada's Sport...

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