Heat Cramps

Michael Johnson warms up for 200-m race at Olympic trials after suffering a heat cramp earlier in the day.

Heat cramps are the most common type of heat-related injuries that are sustained by athletes. The impact of heat upon the function of the human body is a progressive form of injury, with heat cramp being the mildest and most readily treatable form, heat exhaustion the next most significant heat-related occurrence, and the culminating stage of heat injury, known as heat stroke, the final and the most dangerous development.

The cardiovascular system is the first line of defense within the body to combat the effects of heat. Any form of exercise will generate heat through the processes of energy production to power physical movement, no matter what the external environmental conditions may be. In activities taking place in a warm environment, where temperatures affecting an athlete are increased due to air temperature, the athlete's clothing or equipment, or the intensity of the effort, the body temperature will tend to rise beyond the standard of 98.6°F (37°C). The cooling mechanism of the body in response to increased heat is a subtle and sophisticated one; the first response is to attempt to reduce body heat to a point where it is relatively close to that of the surrounding environment. The cardiovascular system is constructed to permit the surface of the skin to be cooled through capillary (small blood vessels) action, in which warm blood, heated through the production of energy, is delivered to the skin surface where the capillaries are located. Warm water, in the form of perspiration, is released through the skin.

The efforts of the body to reduce its internal temperature are not without consequence. Excess perspiration, composed almost exclusively of water, with smaller amounts of sodium, calcium, and other minerals, reduces the amount of fluid available to the volume of blood plasma, the fluid component of blood that forms approximately 90% of its volume. Lesser blood volume will result in a correspondingly reduced ability of the cardiovascular system to deliver oxygen, nutrients, and energy stores throughout the body. This is the state generally known as dehydration.

It is in such circumstances that heat cramps most commonly, although not exclusively, arise. The heat cramp is a form of a forceful muscle contraction or spasm, often quite painful, most frequently observed in a limb that is actively involved in the sport or exercise in question. In runners and cyclists, heat cramps occur in the gastrocnemius (calf) or hamstrings and quadriceps (thigh) muscles. Other symptoms include dizziness or apparent disorientation, weakness, vomiting, skin that is hot and sweaty to the touch, and a rapid heartbeat.

Overexertion of a muscle or muscle group will often be an underlying cause of heat cramps. Also contributing to both the existence as well as the persistence of a heat cramp are a failure on the part of the athlete to properly warm up or stretch out the affected muscle groups, as well as a failure to properly hydrate the body both before and during the activity. There is a documented higher incidence of heat cramps among less-conditioned as opposed to elite-level athletes.

The impact of dehydration on the muscles is a correlation to the optimal balance of water, sodium, and calcium in the system. Sodium and calcium are minerals that are a part of the group of vital substances functioning within the body known as electrolytes, chemicals capable of transmitting electronic signals from the central nervous system to the working muscles. The production of perspiration and the creation of imbalances in the electrolytic system contribute to the creation of heat cramps. The mechanism of heat cramps is such that it is possible, although less likely, to sustain a heat cramp injury in cool weather, as dehydration and electrolyte imbalance can occur in any weather.

Heat cramps should be treated aggressively. The person should immediately be directed to a cooler environment, with moistened towels applied to the affected muscles. The muscles can be stretched gently, but the injured area should not be rubbed or vigorously massaged. Diluted concentrations of electrolytic sports drinks can also be administered to assist in the elevation of mineral levels. Given the strain to which the muscle has been exposed, the athlete should not resume play for at least 24 hours after the heat event. Appropriately treated, heat cramps should have no long-term effect on the athlete.

SEE ALSO Acclimatization; Cardiovascular system; Cramps; Hyponatremia.