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Water Loss—Sweat
Evaporation from the skin, important for controlling body temperature, is also a major source of water loss. Even under cool, resting conditions, about 30 percent of water loss occurs here. Water in exhaled air is also significant, as the air going in and out of your lungs is humidified. A small but significant water loss (about 5 percent) occurs through the intestine.
During training and racing, water loss increases dramatically. The body attempts to conserve water, and loss through the kidneys becomes limited. In this case, sweating increases significantly, and water lost from the skin through sweating is about three hundred times the amount lost during rest. This water loss can be as high as a liter an hour in longer activity. In a typical four-hour event, for example, an athlete can lose about four liters (about a gallon) of water (and a significant amount of sodium). But in a very hot, dry climate, the same event could result in twice the amount of water loss through sweat. It’s very important for athletes to replace this much water throughout the race to avoid stress on the body and reductions in performance.
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Question: What happens when you get an IV after a race? I did the Hawaii Ironman one hot year, and I was amazed to see so many triathletes in the medical tent getting intravenous treatments. How does an IV speed up rehydration? Are there any side effects?
Answer: If you are in need of medical assistance during or after a race (as determined by someone on the medical staff), you may be given an intravenous (IV) solution. Depending on your particular needs, this may provide your body with much needed water, sodium and other electrolytes, and glucose. This procedure can quickly restore these nutrients to your bloodstream to help your body speed recovery. There are no real side effects, other than the rare risk of improper insertion of the needle into your vein or secondary infection. An important point to emphasize is to prevent finishing a race in such poor health.
The amount of water loss during activity is determined in part by a number of factors that include:
- Air temperature (The higher the temperature is, the more water loss.)
- Humidity (Drier climates result in more water loss.)
- Body size (Larger athletes lose more.)
- Level of fitness (Those more fit may regulate water better.)
- Level of health (Those with good adrenal function regulate water better.)
- Heat acclimation (If you’re used to the race climate, you’ll regulate water better.)
- Clothing (Too much or too little during a sunny race, for example, can cause poor regulation.)
Along with water, sweat causes significant losses in sodium. For each liter of water lost in sweat, there is a loss of between one and five grams (1,000 to 5,000 mg) of sodium—as sodium chloride—lost per hour of hard training or competition.
Always stay properly hydrated, especially when racing.
