Top off your fluid level to beat the heat

Stay hydrated to beat the heat and humidity.

It’s summer in Chicago, and that means heat and humidity, which can pose challenges for exercising.

If you are unaccustomed to exercising in these conditions, give yourself a chance to acclimate by building up your workout routine. It generally takes about two weeks for the body to fully adapt to warm weather.

The body typically cools itself by increasing surface blood flow or, on a windless day, relying on mainly evaporation. Add humidity, and our body’s air conditioning system is severely taxed. Maintaining hydration can help. Electrolyte replacement is critical for ultra-endurance events, but for most, the normal diet allows the body to catch up on losses through perspiration.

With heavy exertion, an individual may lose up to 3 pounds of fluid per hour. During exercise, fluid replacement is required at the rate of 150-200 milliliters of fluid every 10 to 15 minutes. For most activities plain water suffices. For those whose exercise interrupts meals, sports drinks supply calories while hydrating. Sports drinks containing 4 to 8 percent glucose sugar are most readily absorbed. Higher glucose concentrations tend to reduce stomach emptying time, possibly leading to cramping. Excessive fructose sugar levels can produce diarrhea.

What you do prior to exertion in the heat also has a big impact on your heat tolerance. Alcohol can increase urine output, dehydrating you. It also can influence blood flow to the skin’s surface, alter the body’s temperature set point, and potentially augment heat stress further by diminished salt and water retention. Try avoiding alcohol for 24 hours prior to competition or exercise. If you do decide to imbibe alcohol post-exercise, rehydrate first and take the alcohol with a meal.

We’re stuck with what weather we’re dealt. How we weather the weather is largely left up to us.

Brian Svazas, M.D., M.P.H.