Thursday, August 4, 2011

Beat the Heat: How to Exercise Safely When the Heat is On

It's summer time! Sunny days, blue skies and warm temperatures mean it's time to be outside and active. However, it is not without risk. Each year, thousands of people experience heat-related emergencies and, unfortunately, several hundred die as a result of heat stroke (it's the second-leading cause of death among athletes). To ensure a safe summer of outdoor exercise and activity, make sure you incorporate the following steps to help beat the heat.

Education is the first step to preventing heat illness. Be aware of the following heat illnesses, which often progress in stages.

Heat Cramps- The mildest, most common heat "syndrome" is called heat cramps. These slow, painful spasms, which can last 1-3 minutes, occur as excessive amounts of fluids and/or electrolytes (potassium and sodium) are lost. Heat cramps occur in the exercising muscles, typically the arms, calves and abdomen. If the individual does not stop to rest and rehydrate, they can progress to heat exhaustion.

Heat Exhaustion - Heat exhaustion is the inability to continue to exercise; the body simply slows to a stop. Signs and symptoms include: cool, pale, moist skin, heavy sweating, headache, nausea and dizziness. The excessive loss of fluids results in the inability of the circulatory and thermoregulatory systems to keep pace with the demands of exercising in the heat. Without the ability to cool itself, life-threatening increases in body temperature occur very rapidly. It can be a deadly mistake to ignore the symptoms of heat exhaustion.

Heat Stroke - This is the most dangerous heat emergency with a death rate of nearly 50%! The signs and symptoms include profuse sweating or the skin may appear red, hot and dry, rapid pulse, vomiting and decreased alertness level or complete loss of consciousness.

If you are going to exercise outside, do so before 10 a.m. or after 4 p.m. Avoid exercising when the temperature is above 85 degrees and the humidity is 75% or higher (high humidity prevents the evaporation of sweat... more about that later). People more susceptible to heat illness are older adults, children, the obese, diabetics and those with heart disease. Also, medication can impair the body's ability to regulate heat. Certain drugs, which include anticholinergics, antihistamines, antidepressants and some tranquilizers, disrupt hypothalmus function and slow sweat production. Cardiovascular drugs can restrict blood flow to the skin (impairing the body's ability to release heat), inhibit compensatory increases in cardiac output or produce a state of dehydration. These include vasoconstrictors, beta blockers and diuretics. Make sure if you are on medication to consult your physician before beginning an exercise program.

One of the best ways to prevent heat illness is to allow the body to get acclimated to exercising in the heat. The process, which takes 10 to 14 days (75% of the adaptation is believed to occur within the first 5 days), involves gradually increasing the intensity and duration of the exercise sessions. In other words, take it easy for the first few workouts as you gradually increase your exposure to the heat. For example, 15 minutes of exercise followed by 15 minutes of rest in the shade. During this process, the body makes several adaptations to enhance its ability to cool itself, including an increase in blood volume to allow the blood to absorb more heat and distribute blood flow more readily, sweating sooner to begin the cooling process earlier, sweating more to enhance cooling, and producing sweat that is hypotonic (fewer electrolytes are lost).

"Drink early and drink often" should be your battle cry to prevent dehydration. Unfortunately, the thirst mechanism is not accurate. You can become dehydrated before you become thirsty, plus your thirst can be quenched before you replace all the fluids that are needed. This is often referred to as "voluntary dehydration" because people drink insufficient volumes of fluid to offset sweat losses (people typically only replace one-half to two-thirds of what is actually needed). So drink before (two glasses within two hours of the workout), during (every 15-20 minutes) and after exercise (2 cups for every pound lost). The general rule of thumb has been if the activity lasts less than 60 minutes, plain water is fine. However, drinking sports drinks, regardless of the duration of the activity, may encourage greater intake because of the added flavor. In addition to flavoring, cold fluids (50 to 59 degrees) also improve palatability, and may aid gastric emptying and heat dissipation. Sports drinks are the preferred recovery beverage because the sodium content maximizes rehydration by helping the body absorb and retain more water. Research has shown that 8 ounces of sports drink with 6 to 8 percent of carbohydrates and 110 mg of sodium absorbs into the body faster than plain water. To determine the percentage of carbohydrates in sport drinks, take the grams of carbohydrates per serving divided by the ml per serving and multiply by 100 determines the percentage of carbohydrates.

During exercise, 80 percent of heat loss is attributed to the evaporation of sweat. Sweat alone does not cool the body; it is the evaporation of the sweat that is critical. When sweat evaporates, the skin temperature goes down, allowing more warm blood to flow to the skin from the core. To enhance this process, remember the "Three L's of Proper Attire": lightweight, light-colored (to reflect the sun's rays) and loose-fitting (to allow adequate air circulation). Wear minimal clothing to allow the skin to be exposed to enhance evaporation. Also use your sunblock; sunburn inhibits the skin's ability to sweat. Common sense is the best bet to prevent heat illness. Be aware of the heat index. If the surrounding air is already warm and heavy with humidity, it cannot absorb extra heat or sweat. Above 75 to 80 percent, relative humidity, heat loss through evaporation will be minimal.

Enjoy the warm weather, but to beat the heat remember the five "Ates"... Educate, Mandate, Acclimate, Hydrate and Evaporate!

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