Whole-Body Heat Cramping

Whole-body heat cramping is a progressive and debilitating physical state, one that tends to afflict athletes who are training or competing in warm weather conditions. Cramping that affects the function of muscle groups throughout the entire musculoskeletal system is a result of the same mechanisms that trigger more localized and painful muscle cramping, which is typically isolated in the calf and hamstrings.

Muscle cramps are caused by the combined operation of sodium deficit, muscle fatigue, and dehydration. The primary cause of muscle cramps is a deficit in sodium, the essential mineral and electrolyte that is obtained from a variety of dietary sources. In hot weather, sodium is lost through the increased levels of perspiration generated by exercise, as the body endeavors to maintain a healthy internal temperature through the cooling release of sweat. When the body perspires, sodium (and trace amounts of other minerals, such as calcium and magnesium) and water are passed together from the body.

Muscle cramps rarely occur in a strong and rested muscle. Cramps invariably become a factor in athletic performance after the muscle has endured significant stress.

When the factors of sodium depletion, dehydration, and muscle fatigue are combined, muscle cramping is a real risk. The cramps occur because the body requires sodium to perform two critical tasks that are especially relevant to warm weather athletic performance: the maintenance of fluid levels, particularly blood volume, throughout the body (the process of osmoregulation), and the ability of the nervous system to transmit the nerve impulses that are required to initiate the muscular contraction necessary to produce movement. The ratio between total body fluid volume and sodium is the key marker relied on by the body to determine how much fluid should be present. When the proportion of sodium to body fluid is too low, the body will resist the absorption of further water or other fluids, which can initiate a dangerous physical condition known as hyponatremia. When there is too great a level of sodium relative to fluids present in the body, the body senses that it is dehydrated, which will signal the kidneys to reduce the production of urine. The thirst mechanism is also activated at this time.

The athletes most prone to whole-body cramping are those who have a relatively low body fat percentage, with a relatively high proportion of fast-twitch muscle fibers. All athletes who become dehydrated to the relatively modest amount of 2% of their total body weight during the course of a warm weather activity are at risk of developing muscle cramps.

Muscle cramping that occurs to any extent in the body, also referred to as heat cramps, is the least serious of the well-recognized heat illnesses that may befall athletes in warm weather conditions. Heat exhaustion is the cumulative effect of heat exposure that prevents the body's thermoregulatory mechanism from effectively dispersing the internal heat generated by exercise. Heat stroke is the most serious and the potentially fatal failure of the body to prevent overheating, leading ultimately to a shutdown of organ function, and a significant risk of permanent damage to the heart or liver.

Sodium depletion that leads to whole-body cramping takes place even though most athletes consume far in excess of the required and recommended daily allowance of dietary sodium. The body does not store sodium for indefinite periods, as it does fat-soluble substances such as vitamin D. Excess sodium, while capable of unduly stressing the cardiovascular system, primarily through the high blood pressure that is a byproduct of the osmoregulatory process in sedentary persons, is excreted as urine.

The first line of defense to whole-body heat cramping is built in the period prior to the start of warm weather sports. The introduction of any athlete to an unaccustomed warm environment must be gradual, both in terms of training volume and training intensity, to permit the acclimatization of the athlete to the environment. For most athletes, the heat acclimatization process will be over 90% complete within 10 to 14 days of its commencement. The more efficient the function of the cardiovascular system in warm weather, the better the body will maintain the necessary blood volumes during exercise, subject to proper hydration practices.

The second component to the prevention of debilitating whole-body cramps is the implementation of a rigorous hydration strategy. Athletes must be directed and encouraged to consume appropriate levels of fluids prior to, during, and subsequent to all training and competitions. Fluids that contain sodium, or water consumed along with a salt tablets (regular salt is 40% sodium by weight), are a preferred rehydration choice to that of water alone during warm weather, due to the actions of the body to preserve its desired osmoregulation.

A defined hydration strategy is of supreme importance in sports that employ a two-a-day practice regime in warm weather training. American football is a prime example; football carries with it an additional cramping risk, due to the full equipment, which has a significant additional weight and covers the body from the knees to the top of the player's head, preventing heat from dissipating.

The most effective remedy for whole-body cramping is immediate rest from the activity, the placement of the athlete in a cool environment, and the consumption of appropriate replacement fluid. Playing through these often-debilitating cramps is likely impossible, and if the athlete attempts to force further strenuous movement from tissues that have sustained sodium depletion, the athlete is at risk of causing more serious muscular injury.

SEE ALSO Cramps; Heat cramps; Muscle cramps; Sodium and sodium deficits; Thermoregulation, exercise, and thirst.