The human body, being warm blooded, maintains a fairly constant internal temperature, even though it is being exposed to varying environmental temperatures. To keep internal body temperatures within safe limits, the body must get rid of its

excess heat, primarily through varying both the rate and the amount of blood circulation through the skin and the release of fluid onto the skin by the sweat glands. These automatic responses usually occur when the temperature of the blood exceeds 98.6F and are kept in balance and controlled by the brain. In this process of lowering internal body temperature, the heart begins to pump more blood, blood vessels expand to accommodate the increased flow, and the microscopic blood vessels (capillaries) which thread through the upper layers of the skin begin to fill with blood. The blood circulates closer to the surface of the skin, and the excess heat is lost to the cooler environment.

If heat loss from increased blood circulation through the skin is not adequate, the brain continues to sense overheating and signals the sweat glands in the skin to shed large quantities of sweat onto the skin surface. Evaporation of sweat cools the skin,

eliminating large quantities of heat from the body.

As environmental temperatures approach normal skin temperature, cooling of the body becomes more difficult. If air temperature is as warm as or warmer than the skin, blood brought to the body surface cannot lose its heat. Under these conditions, the heart continues to pump blood to the body surface, the sweat glands pour liquids containing electrolytes onto the surface of the skin, and the evaporation of the sweat

becomes the principal effective means of maintaining a constant body temperature.

Sweating does not cool the body unless the moisture is removed from the skin by evaporation. Under conditions of high humidity, the evaporation of sweat from

the skin is decreased, and the body’s efforts to maintain an acceptable body temperature may be significantly impaired. With so much blood going to the external surface of the body, relatively less goes to the active muscles, the brain, and other internal organs; strength declines; and fatigue occurs sooner than it would otherwise. Alertness and mental capacity are also affected, along with slippery fingers, dizziness, dehydration, and fogging of glasses.

Increased body temperature and physical discomfort can promote irritability, anger, and other emotional states which sometimes causes the overlooking of  safety procedures or the diverting of attention from potential hazards.

Heat stroke is the most serious of health problems associated with cycling in hot environments. It occurs when the body’s temperature regulatory system fails and sweating becomes inadequate. The body’s only effective means of removing excess

heat is compromised with little warning to the victim that a crisis stage has been reached.

A heat stroke victim’s skin is hot, usually dry, red, or spotted. Body temperature is usually 105oF or higher, and the victim is mentally confused, delirious, perhaps in convulsions, or unconscious. Unless the victim receives quick and appropriate

treatment, death can occur.

Any person with signs or symptoms of heat stroke requires immediate hospitalization. However, first aid should be immediately administered. This includes removing the victim to a cool area, thoroughly soaking the clothing with water, and vigorously fanning the body to increase cooling. Further treatment at a medical facility should be directed to the continuation of the cooling process and the monitoring of complications which often accompany the heat stroke. Early recognition and treatment of heat stroke are the only means of preventing permanent brain damage or death.

Heat exhaustion includes several clinical disorders having symptoms which may resemble the early symptoms of heat stroke. Heat exhaustion is caused by the loss of large amounts of fluid by sweating, sometimes with excessive loss of salt.

A person suffering from heat exhaustion still sweats but experiences extreme weakness or fatigue, giddiness, nausea, or headache. In more serious cases, the victim may vomit or lose consciousness. The skin is clammy and moist, the complexion

is pale or flushed, and the body temperature is normal or only slightly elevated.

In most cases, treatment involves having the victim rest in a cool place and drink plenty of liquids. Victims with mild cases of heat exhaustion usually recover spontaneously with this treatment.

Those with severe cases may require extended care for several days. There are no known permanent effects.

Heat cramps are painful spasms of the muscles that occur among those who sweat profusely in heat, drink large quantities of water, but do not adequately replace the body’s salt loss. The drinking of large quantities of water tends to dilute the body’s

fluids, while the body continues to lose salt.

Shortly thereafter, the low salt level in the muscles causes painful cramps. The affected muscles may be part of the arms, legs, or abdomen, but tired muscles (those used in performing the work) are usually the ones most susceptible to cramps. Cramps may occur during or after cycling and may be relived by taking salted liquids by

CAUTION: Persons with heart problems or those on a low sodium diet who do physical activity in hot environments should consult a physician about what to do under high-heat conditions.

A person who is not accustomed to hot environments and who stands erect and immobile in the heat may faint. With enlarged blood vessels in the skin and in the lower part of the body due to the body’s attempts to control internal temperature, blood

may pool there rather than return to the heart to be pumped to the brain. Upon lying down, the person should soon recover. By moving around, and thereby preventing blood from pooling, the person can prevent further fainting.

Heat rash, also known as prickly heat, is likely to occur in hot, humid environments where sweat is not easily removed from the surface of the skin by evaporation and the skin remains wet most of the time. The sweat ducts become plugged, and a skin rash soon appears. When the rash is extensive or when it is complicated by infection, prickly heat can be very uncomfortable. This condition can be prevented by resting in a cool place part of each day and by regularly bathing and drying the skin.

Transient heat fatigue refers to the temporary state of discomfort and mental or psychological strain arising from prolonged heat exposure. Persons unaccustomed to the heat can suffer a decline in task performance, coordination, alertness, and

vigilance. The severity of transient heat fatigue will be lessened by a period of gradual adjustment to the hot environment (heat acclimatization). Humans are, to a large extent, capable of adjusting to the heat. This adjustment to heat, under normal circumstances, usually takes about 5 to 7 days, during which time the body will undergo a series of changes that will make continued exposure to heat more endurable.

On the first day of performing in a hot environment, the body temperature, pulse rate, and general discomfort will be higher. With each succeeding daily exposure, all of these responses will gradually decrease, while the sweat rate will increase. When the

body becomes acclimated to the heat, the person will find it possible to be active with less strain and distress. However, persons who return to heavy activity after a leisurely vacation in a cooler climate or after an extended illness may be seriously affected by the heat.

It should be readily apparent that heat-related issues should not be treated lightly. Understanding the demands that heat makes on our bodies should make it clear that proper precautions must be taken to effectively tolerate the hot Texas summers. At this point in the cycling season, everyone has hopefully adjusted to the heat and realized the importance of hydration and keeping as cool as possible. We can all continue to be vigilant of ourselves and our fellow cyclists as we ride through the summer. Cooler times are not far off!