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By Dave DiFabio
With the hot, hazy days of summer coming, extra precaution is needed reduce the risk of a heat related illness while exercising outdoors. On average, most people tend to only replace 2/3 of the water they sweat off during exercise. According to the Food and Nutrition Board, the average male should consume almost 4 liters of water per day and women should consume almost 3. Sweat loss can increase these recommendations significantly. For example, some athletes can lose 1.8 liters of water/hour during prolonged exercise in the heat.
Sweat loss is tracked by a decrease in body weight during a single workout. Fat loss will not happen that quickly. Therefore, a loss of body weight during a workout would be due water lost through sweat. A 1% decrease in body weight can be associated with an elevation in body temperature. A 3 to 5% loss would results in cardiovascular strain and an impaired ability to dissipate body heat. At 7% loss, you're likely to collapse.
The good news is that fit people actually sweat MORE, thus allowing more efficient cooling of the body. So as you get into better shape you can also become more acclimated to the heat.
One step you can take towards getting acclimated to the heat is to assess your body's hydration status and then adjust your fluid intake accordingly. Before you workout, step on the scale in the buff. After your workout, assess it again in the buff. Each pound of body weight lost during the workout represents a 1/2 liter of lost water. This must be replaced before the next workout. Any athlete that has lost 5 to 10 lbs of weight during the week can be classified as chronically dehydrated. Again, this is because 5 to 10 lbs of fat loss is not possible in one week so the weight loss represents lost water.
Sweat also contains electrolytes, which are essential to nerve conduction and muscle contractions. The average concentration of sodium in sweat is 1.15 grams/liter of sweat. This could range anywhere from.46 to 2.3g/L depending on your fitness level. As you get into better shape your body becomes better at retaining electrolytes despite the fact that fit people sweat more. American's usually consume 4 to 6 grams of sodium everyday thanks to foods such as pizza, ham, and potato chips. This is usually more than enough without the consumption of sports drinks.
Potassium lost during sweat can usually be replaced with 2 to 6 grams per day. The average American intake is 2 to 4 grams. Most people need to be encouraged to eat more citrus fruit, melons, strawberries, tomatoes, and bananas. Meat, potatoes, and milk are good sources too.
Below are some recommendations to stay hydrated and maintain electrolyte balance:
Drink 1/2 liter (1 pint) of fluid 2 hours before activity.
Drink 6 to 8 ounces, every 15 minutes during activity and start drinking BEFORE feeling thirsty.
Cool water works just fine. 50 to 70 degrees Fahrenheit seems to be absorbed quickest. Unless you're exercising longer than an hour you might not need a sports drink. Avoid standard soft drinks because they have too much sugar per serving. This will slow the absorption of the sugar and fluid into your blood stream where it is needed most.
After the workout assess your weight loss as previously described and drink 1/2 liter (1 pint) of fluid for every pound of body weight lost.
To replenish the electrolytes lost during exercise you should eat a full meal comprised partially of the whole foods mentioned above. Sports drinks can only replace a fraction of the total amount. If you relied solely on a sports drink to maintain your electrolyte balance, you'd have to drink a ridiculous amount. The amount of sodium (110 mg) in a single serving of a sports drink is enough to do two things. First it will help you retain more fluid while you're hydrating during your workout. Second it's enough sodium to make your thirsty enough to drink more. Pretty ingenious isn't it?
Till next time.... Train Like You Play & Play Like You Train
Dave DiFabio MA, CSCS, USAW
Owner/Strength & Conditioning Coach - Team Speed Fitness LLC
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