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The Midwest muggy summer is around the corner. “Weekend Warriors” and seasonal outdoor workers should be concerned with one question: What fluid is right for preventing dehydration and problems from the heat?

Working muscles produce heat as a byproduct of metabolism. Evaporation of sweat at the skin is the body’s cooling process. Blood vessels just below the skin are cooled by the evaporation, and the rest of the body is cooled as the blood returns through the deeper organs. Sweat evaporates less in hot, humid conditions. Without evaporation, there is little cooling and body heat builds, increasing sweating and fluid loss. Just one percent of body fluid loss can cause symptoms of lightheadedness and dehydration. Mild dehydration causes fatigue, decreased coordination and cramping.

Heavy exertion can cause a loss of 1.5 liters or more of fluid each hour of activity. To prepare for the loss associated with activity, a person must pre-hydrate. In hot weather, the body may not keep up with sweat losses and dehydration may be inevitable. Pre-hydration ensures maximal hydration at the start.

Pre-hydrate beginning two hours before exercise or performance. Cool water is the fluid of choice, except in cases of extreme endurance (greater than 90 minutes exertion). In that case, a sports drink with electrolytes may be beneficial. Start with three cups (250 ml) two hours before, two cups 10 to 15 minutes before, one cup every 15 minutes during activity and two cups after exercise.

While the “old school” thought was to withhold fluid and allow the body to adapt, this practice was false and dangerous. Full hydration optimizes performance, does no harm and may be protective.

What fluid is best to prevent dehydration during activity?

For most, plain cool water between 59 and 72 degrees is best. This helps to cool the body from the inside. Water is rapidly absorbed and transferred to muscles by the GI system. Replacing electrolytes and using carbohydrate drinks can inhibit the transfer because of the extra effort needed by the GI system, possibly affecting endurance, leading to stomach cramping.

However, sports drinks do have advantages for workers strenuously exercising for 90 minutes or more at a time, replacing simple sugar carbohydrates and electrolytes. This helps maintain optimal muscle contraction and prevents fatigue. Replacing the electrolytes prevents hyponatremia (low blood salt concentration). Most activity of less than one continuous hour can be replenished with a nutritionally balanced diet. For most athletes, water is more beneficial and causes less stomach upset.

Caffeine can boost performance for a short time, but it acts as a diuretic and can increase your risks of becoming dehydrated. Caffeine can also increase heart rate and change the heart’s performance properties. Plain, cool water is best. IBI

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