Getting it Straight: Heat Stroke, Heat Cramps, Heat Exhaustion

The onset of warmer weather is a sure thing, now that the snow is melting. There is always confusion among many of us over the differences between heat stroke, heat cramps, and heat exhaustion. So let us take the opportunity to review those conditions and get them straight.

Every year we read of athletes and ordinary people collapsing from the heat and being rushed to the emergency room. Heat can kill. A few years ago we were shocked to read of the death of a Minnesota Vikings player during training camp. On July 30, 2001, Corey Stringer left the field on the first day of training camp with symptoms of severe heat strain (nausea, dizziness, vomiting). On the second day of camp, July 31, he collapsed and was rushed to a hospital only to die about 13 hours later.

First we need to describe the body's reaction to heat stresses, and describe the kinds of temperature measurement. Air temperature is just one component of 'Temperature'. Temperature as experienced by a human body is actually composed of four variables:

1. Air Temperature
2. Humidity
3. Wind Speed
4. Thermal Radiation

How did those four factors affect Corey Stringer's ability to cope with heat? We know it was a hot, cloudless day. The heavy padding and tight pants limit the ability to lose heat, and macho guys often skip drinking fluids because they think they can tough it out. Football players in particular start training for their sport in the hottest part of the year, and are not acclimated to the heat.

Thermal radiation refers to the fact that some surfaces absorb more heat than others. People wearing black shirts will certainly feel a lot warmer than those wearing light colors. Air velocity or wind speed factors in due to the cooling effect of sweat evaporating off one's skin. Sweat that is dripping off your face does not cool you; you need a fan or a breeze to help it evaporate off your skin.

There is actually an equation to calculate the effect of the above four variables. The Wet Bulb Globe Temperature (WBGT) equals 0.1 Tdb plus 0.7 Twb plus 0.2 Tg. The Wet Bulb Globe Temperature was devised in the 1970s to incorporate the effects of all four variables (conduction, convection, evaporation and radiation) to measure the cooling capacity of the environment.

T is temperature. Tdb is temperature as measured by the dry bulb thermometer, or in other words the objective temperature. Twb is temperature as measured by a wet bulb, to capture the cooling effect of evaporation; it is kept moist and so as the moisture evaporates, its temperature is lower than that of the dry bulb. Then there is the Tg, temperature as measured by a thermometer inside a black balloon-like globe; it measures the effect of radiation heat. .

Heat Cramps

This is the least serious of the three heat-related disorders, although that is not much consolation to anyone who has suffered through its painful cramps. These cramps affect the large muscles, whichever ones are used most in your sport; runners get cramps in the large leg muscles, for example. This is caused by sodium losses and dehydration in those who sweat heavily.

They can be avoided or lessened by sipping water during exercise and adding liberal amounts of SALT to ones food. Potassium is not a major factor in heat cramps and so eating bananas will accomplish little. Those stricken by heat cramps are usually moved to a cool location and given an intravenous saline solution.

Heat Exhaustion

Heat exhaustion is the next level. Victims feel dizzy, nauseated, tired and may vomit or faint. The pulse may be weak and rapid. The cardiovascular system is struggling to do its job despite severe dehydration. It is almost like a positive feedback loop, where dehydration causes vomiting which aggravates the dehydration. We usually see cases like this in people who are trying to lose weight quickly with extreme exercise, thinking that they can 'sweat it off'.

Heat exhaustion occurs because there is not enough blood volume to dissipate heat quickly enough. Blood volume is being depleted because sweat comes mainly from blood plasma. Your muscles and skin are competing for a diminishing volume of blood to either pump oxygen to the muscles or to cool the skin. Core temperatures can be well below the 39 degree tipping point and still the victim has collapsed.

Treatment for victims is similar to those with heat cramps: moving to a cooler room and administration of saline solution (if conscious, orally, and if unconscious via an IV).

Heat Stroke

Heat stroke is a life-threatening disorder. The internal body temperature rises above 40 degrees Celsius (104 degrees Fahrenheit). Sweating has ceased, and the pulse and breathing may be rapid. The person may be confused, disoriented or unconscious. The reason for altered mental states is that the brain is sensitive to extreme heat. The body must be cooled down because it can continue to rise and lead to coma or even death.

One of the most effective ways to cool a body is immersion in cold water. If a tub is not at hand, then wrapping the person in cold, wet sheets is another technique.

Hyperthermia and Hyponatremia

Hypothermia is more familiar to us than its counterpart, hyperthermia. An internal body temperature above 40 degrees Celsius (104 degrees Fahrenheit) is entering a danger zone. It is one of the definitions of Heat Stroke.

Hyponatremia is a very low level of sodium in the blood; specifically, lower than the normal range of 135-145 mmol/L. It too, is a life-threatening condition.

Athletes who are in hard training need to replenish fluids continuously or before and after exercise. After exercise, the rule of thumb is to drink 16-24 ounces of fluid for every pound lost during that exercise session. The reason for hydrating is not only to keep within the ideal range for saline content, it is also to help cool your body.

The boundary has been shown in studies to occur at about the 45 minute mark. If you plan to exercise longer than 45 minutes, then you definitely need to hydrate as you go in order to keep your body temperatures from rising to a dangerous level.

It can take nine to 14 days of exercising in hot weather (an hour or more each day) before one becomes acclimated to the heat. What is acclimation? There are two processes that help one to cope better with heat. One is that the sweat glands actually conserve more sodium. Your sweat becomes less salty although it may taste the same on your tongue.

The other adaptation is that your body's plasma volume increases along with increased sweating. Also people who are already fit can adapt to heat better than those who are couch potatoes.

The smart athlete, whether he or she is a dedicated fitness buff or a weekend warrior, can find many useful tips in the research into sports physiology.

Source: a textbook titled Physiology of Sport and Exercise, Fourth Edition, by Wilmore-Costill-Kennedy, published by Human Kinetics, 2008. You may also go to their website at HumanKinetics.com