With the hot summer months looming up on us, we should remind ourselves of the single most serious threat to a runners' life - heat injury. The fatality rate from heat problems is higher than sudden death from heart attacks or being killed by automobiles while running.
Although elite athletes have heat issues occasionally, semi-conditioned rank and file runners are most susceptible to heat injury. Even dehydration can lead to unconsciousness and death if allowed to escalate into heat exhaustion or heat stroke.
Overheating will always be a limiting factor to our endurance performance. Unfortunately, each summer thousands of runners discover this the hard way and for some, it's a fatal experience.
Causes of Heat Injury
Let's examine the factors that combine to cause heat injury: air temperature, air movement, humidity, exposure to the sun, acclimatization and the intensity or duration of your run.
We can generally tolerate temperatures as high as 80-90 degrees F. because we can sweat as much as two liters per hour. In dry air most of this sweat evaporates, thus cooling the body. However, as humidity increases, the saturated air absorbs less sweat and it pools on your skin, so body heat builds up. So on humid, muggy days, you'll need to drink more water and run at a slower pace to allow for this.
The greater the air movement around us, the greater the cooling effect, because air currents enhance evaporation. A headwind helps evaporation but a tailwind actually reduces the airflow over the body, hindering evaporation. On hot days, you might consider running into a slight breeze to encourage more evaporation. However, running into strong headwinds causes you to work harder, so you should draft behind other runners in this situation.
Sunlight acts like an insulating blanket by warming the skin--so direct sunlight causes a rapid rise in your body heat. Heat is carried from your core to your skin via blood. Here, evaporating sweat cools the blood before it returns to your core.
Skin temperature must always be at least two degrees cooler than your core temperature to allow for a cooling heat gradient, so you run into problems when your skin absorbs heat faster than evaporation can cool it. Where possible avoid direct sunlight when running on sunny days.
Even fit runners can only tolerate a narrow range of internal core temperatures. The good news is that a fit person can tolerate a higher core temperature than an inactive person, so heat injury usually arise when runners are inadequately conditioned for a race or push beyond their limits.
Your workout intensity and the length of your workout contribute to heat stress production. Your body isn't efficient when you exercise - 75% of your expended energy is turned into heat. Thus the faster and longer you run, the greater the heat load placed on your body.
Your previous exposure to heat is also a major factor in determining your susceptibility or resistance to heat injury. Through training you can partially (but never completely) adapt your thermoregulatory mechanism. This is called acclimatisation. To complicate the matter more, people respond differently to heat, so adjustments to exercising in heat should be made depending on how you personally handle heat.
A combination of two or more of the above factors increases your risk of heat injury. The most formidable combination is elevated heat and humidity. An air temperature of 60 degrees plus 95% humidity is more dangerous than a "dry" 85 degrees, for example. Such combinations place an extra burden on our cardiovascular and thermoregulatory systems. It's no coincidence that runners with undetected cardiac problems "choose" hot races to collapse in.
The Biology of Heat Injury
The hypothalamus-the body's thermostat-detects heat buildup and responds by dilating the blood vessels in the skin to be cooled. It also makes the heart pump faster to shunt more blood to the surface, causing your sweat glands to produce more sweat.
Soon a vicious competition for blood ensues 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 or foolhardy runner makes a mistake. Instead of slowing down, they keep pushing themselves.
Doing this dehydrates the runner further. With this increased sweat loss, the plasma becomes thicker and more viscous, causing the heart to pump harder. Continuing sweating without taking in adequate fluids amplifies these demands on the circulatory system, which are by now becoming intolerable.
Usually running performance declines by this stage, pressuring the over competitive runner to pick up his pace. At this stage the runner becomes a prime candidate for heat exhaustion, or worse, heat stroke. The competition for blood has become unbearable, and the circulatory system and hypothalamus shut down. Blood pressure drops. Unconsciousness. Possible death.
Now that you understand the mechanisms involved in hyperthermia, you'll need to recognize the signs and symptoms in yourself (and others). Warning signs of heat exhaustion include dizziness, profuse sweating, weakness, dehydration, parched throat and hot red skin.
Warning Signs and Treatment of Heat Injury
Warning signs of heat stroke are headaches, dizziness, disorientation, nausea, pale, dry skin, decrease in (or stop) 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 Exhaustion
1. Stop! Do not try to run through these symptoms.
2. Find shade and pour water on the victim.
3. Seek medical help.
4. Raise your legs to get blood to the brain. (Raise heels 8-12 inches)
5. Keep victim lying down.
6. Give victim cold water to drink for 1 hour.
7. Loosen or remove clothing.
8. Sponge bare skin with cold water or rubbing alcohol.
9. Use fan or air conditioner to create draft over victim's body.
Treatment of Heat Stroke
1. Same as 1-5 above.
2. Treat for shock, but do not cover victim with blankets.
3. Take immediate measures to cool body quickly as for steps 7, 8 and 9 above.
4. Or apply cold ice packs or ice continuously.
5. Or place victim in tub of cold water.
Prevention of Heat Injury
Generally males 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 a long run or race. Wear light colored clothing that breathes well (cotton) and repels the sun's rays.
On hot or humid days don't start too fast for your current level of fitness, and don't push beyond your limits under these conditions. Know your current state of fitness and be adequately conditioned for your race-if you aren't, don't compete.
Be wary of races organized by local charities-they may be directed by amateurs who have no idea of the dangers of heat stroke, and may have inadequate precautions for these eventualities, such as not enough water at drinks stations, no medical coverage, etc.
Drink lots of cold water before, during and after your training and racing efforts. Make sure you eliminate excess water from the bladder a half hour before you run, then drink 200-500 mls 15 to 20 minutes before show time. Try to drink at least one cup of water every 20 minutes during the run. Don't wait until you're thirsty--it will be too late. Drink during your training runs to get used to it. If you live in the Midwest, South or East coast this is necessary for your survival anyway.
Keep your body wet. The temporary relief is well worth it. Putting ice under their cap is an old trick used by seasoned marathoners. On hot, muggy days don't try to stick to your planned distance. Be prepared to cut back if conditions are dangerous. Try to run in cooler shaded areas on hot days. Another precaution is to run with a partner and keep an eye on each other.
For good acclimatization, run at least three days a week in conditions similar to those you'll race in. If you can't do this, avoid races held in the heat of the day. Early morning and evening runs will not fully prepare you for the midday heat. You'll need to allow 10-14 days of slow, progressive running to adjust to the heat.
The benefits of acclimatization are less sweating at a given workload, and less elimination of electrolytes in your sweat. Are salt tablets necessary? Some research has shown the chloride in table salt can inhibit your body's ability to deal with heat stress, so high levels of salt intake may not be necessary, or may even be counterproductive. You'll get adequate salt intake from your meals, even without salting them.
Alcohol should be avoided because of its diuretic effect-it causes you to dehydrate quicker. Wearing rubber or nylon sweat suits on hot days is an extremely dangerous practice. People do this to "sweat off" pounds, but this weight loss is fluid loss and is replaced as soon as you drink water.
Electrolyte replacements drinks are highly advanced these days, and lots of research has gone into their efficacy. However, watch out for the imposters that are simply loaded with sugar and no better for you than soft drinks. One problem that runners may encounter with electrolyte drinks is that they are too concentrated, causing nausea. If you find these drinks to sweet or salty, dilute them 100% or more to make them palatable.
Lastly, there is nothing macho or intelligent about shunning water on your racing or training efforts. This practice is detrimental to performance and can lead to heat injury.
Recognition of the signs, symptoms and treatments of heat exhaustion and heat stroke is half the battle in dealing with heat injury. Knowing these signs could save your, or a fellow runner's life. It's a good idea to be familiar with these guidelines to prevent unnecessary hyperthermia. Use this knowledge to prevent you running into problems when exercising outside in hot and humid weather.