Heat Injury:
What Outdoor Athletes
Need to Know
Training and Competing

in the Heat
By Roy Stevenson

With the hot summer months looming up on us, it’s time to review the single most serious threat to the outdoor exerciser’s life — heat injury. It sidelines thousands of outdoor athletes every year with heat illness. The semi-conditioned outdoor enthusiast is most susceptible to heat injury.

Factors contributing to heat stress are air temperature, air movement, humidity, exposure to the sun, acclimatization and the intensity or duration of your exercise session or competition. We can generally tolerate temperatures as high as 80-90 degrees F. because we’re able to sweat as much as two liters per hour. In dry air, most of this sweat evaporates, cooling the body as it does so, however, in Las Vegas, you will quickly dehydrate because sweating stops when there is no longer water available.

Direct sunlight elevates skin temperature, causing a rapid rise in body heat. Our skin temperature always needs to be at least two degrees cooler than the core temperature to permit a cooling heat gradient.

The intensity and the length of your outdoor activity, whether hiking, climbing, running, or cycling, all contribute to heat injury. We generate tremendous amounts of heat during exercise and because the human body isn’t particularly efficient, 75% of our energy turns into heat. Thus the faster and longer we exercise, the higher the heat load placed on our body.

Acclimatization, or our previous recent exposure to heat is also a major factor in determining how we handle heat. Through training, our thermoregulation mechanism partially adapts to heat; but people respond very differently to heat, so individual adjustments to participating outdoors have to be made.

Even fit athletes can only tolerate a narrow range of internal core temperatures. However, fit people tolerate a higher core temperature than inactive people, so heat problems arise when poorly conditioned outdoor enthusiasts push beyond their limits.

A combination of the above factors greatly increases your risk for heat injury, worst combination being high heat and humidity. An air temperature of 60 degrees plus 95% humidity is more dangerous than a “dry” 85 degrees. In this situation, heat is carried from the body core to the skin, where evaporating sweat cools the blood before its returns to the core. However, when your skin absorbs heat faster than evaporation cools it, you run into problems. The hypothalamus—the body’s thermostat—detects this discrepancy and responds by dilating the skin’s blood vessels to cool it more. The heart pumps faster to shunt more blood to the surface, causing your sweat glands to produce more sweat.

By now you have a vicious competition for blood between the brain (which needs 25% of heart output to function) and the working muscles, which need more blood but are getting less and less. It’s here the inexperienced athlete makes a mistake—instead of slowing down, they keep pushing themselves—whether it’s a hike in the woods, an outdoor training run, or mountain biking. By continuing to push, they get more dehydrated and the plasma becomes thicker and more viscous, causing the heart to pump harder. This extra burden on the cardiovascular and thermoregulatory systems often cause people with undetected cardiac problems to collapse.

Continued sweating without taking in adequate fluids, causes an intolerable demand on the circulatory system. So now you’re a prime candidate for heat exhaustion. Watch for these warning signs: dizziness, profuse sweating, weakness, dehydration, parched throat and hot red skin.

Treatment of Heat Exhaustion:

* Do not try to compete through these symptoms. Stop!
* Find shade and pour water on the victim
* Seek medical help
* Raise your legs to get blood to the brain. (Raise heels 8-12 inches)
* Keep victim lying down
* Give victim cold water to drink for 1 hour
* Loosen or remove clothing
* Sponge bare skin with cold water or rubbing alcohol
* Use fan or air conditioner to create draft over victim’s body

If you ignore these signs you’re closing in on heat stroke. Your performance has declined badly by now, often pressuring over-competitive athletes to pick up their pace. Then, the competition for blood becomes unbearable and your circulatory system and hypothalamus shut down. Blood pressure drops. Unconsciousness. Possible death. Watch for these warning signs of heat stroke: headaches, dizziness, disorientation, nausea, pale dry skin, decrease in sweating, fatigue, blurred vision, pounding head, fainting and tingling sensation (goose bumps) on the trunk. Here’s how to treat these symptoms.

Treatment of Heat Stroke:

* Same as 1-5 above, plus:
* Treat for shock, but do not cover victim with blankets
* Take immediate measures to cool body quickly as for steps 7, 8 and 9 above
* Or apply cold ice packs or ice continuously
* Or place victim in tub of cold water

Guidelines for Preventing Heat Injury

* Males tend to handle heat less efficiently then females, as do larger people who have less cooling surface per pound of body weight than slim people. Food digestion interferes with the blood flow to the working muscles, so avoid large meals before running, hiking, climbing or cycling in the heat.

* Wear opaque, light colored, sun protective clothing that breathes well and repels the sun’s rays.

* On hot, humid days don’t push your pace beyond your current level of fitness. Know your current state of fitness and be properly conditioned for your activity. If you aren’t fit and conditioned, don’t compete or go out in the blazing sun.

* Drink lots of cold water before, during and after your training and outdoor exercise efforts. Drink 200-500 mls 15 - 20 minutes before starting and drink at least one cup of water every 20 minutes during your activity. Don’t wait until you’re thirsty—this is too late.

* Keep your body wet. An old trick used by seasoned marathoners is to put ice under their caps. On hot, muggy days don’t try to stick to your planned training distance.

* Be prepared to cut back if conditions are dangerous or try to exercise in cooler shaded areas. On some days you may have to shorten your hike, or completely bag it—so work out in your local fitness club.

* For good acclimatization, exercise at least three days a week in conditions similar to those you’ll participate in. You’ll need to allow 10-14 days of slowly progressive exercise to adjust to the heat.

* Electrolyte sports drinks with sodium have been found to help endurance athletes retain water in their system, so you’re well advised to try them. But watch out for the imposters that are loaded with sugar and no better for you than soft drinks. If electrolyte drinks make you feel nauseated, they’re too concentrated, so dilute them 100% or more.

* Avoid alcohol—its diuretic effect causes you to dehydrate quicker.

* Lastly, there is nothing macho or intelligent about shunning water on your outdoor activities or training efforts. This practice is most detrimental to performance and can lead to heat injury.

Recognition of the symptoms and treatments of heat exhaustion and heat stroke, and knowing how to treat them is half the battle to dealing with heat injury. Be familiar with these guidelines to prevent hyperthermia—it could save your life.

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