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A cramp is a sensation that may be experienced by an athlete in a number of different bodily systems. Typically caused by an involuntary contraction of muscle tissues, cramps that occur during competition are especially common among endurance athletes, such as marathon runners, cyclists, and triathletes.

The most common forms of cramps are muscle cramps, occurring either during or immediately after exertion by working muscles; stomach cramps, which often occur during competition, as opposed to training sessions; and menstrual cramps, experienced by some female athletes (and nonathletes) during their menstrual cycle, when the additional blood generated by the body in the female menstrual cycle passes through the cervix (the narrow portion of the uterus where it joins the vagina).

Muscle cramps are one of the most common injuries sustained in sport. This condition is usually one of short duration, and it tends to respond well to immediate treatment. A muscle cramp is an involuntary spasm or contraction of the muscle fiber that occurs during or immediately after strenuous physical activity. The cramp is often quite painful, to the point of disabling the affected muscles and rendering the athlete unable to continue without medical attention. The cramp will first appear as if the tissue below the skin has hardened, with the skin drawn tightly over the muscle. The calf muscles (the gastrocnemius and soleus) are particularly vulnerable to cramping as they are actively engaged in the generation of movement in all running, skiing, jumping, and cycling disciplines. It is estimated that in the endurance sports, which involve the utilization of the aerobic energy system, between 30% and 70% of participating athletes will suffer from disabling cramps at some point of their athletic career.

Muscle cramps, which may exist alone or in combination, are caused in the following circumstances: fatigue or overexertion; dehydration; low levels of the minerals potassium, calcium, sodium, or magnesium; ingestion of various types of medications; excessive consumption of caffeine; or failure to properly warm up and stretch the muscles

When an athlete has not properly prepared the body for a physical activity through the combined effect of proper pre-event hydration and carbohydrate consumption, the likelihood of muscle cramp is much greater. Inadequate carbohydrate consumption prior to competition will create correspondingly reduced levels of glycogen, the stored sugars that the body utilizes for the creation of the fuel adenosine triphosphate (ATP). Without adequate production of ATP, the muscle will become prematurely fatigued, which can lead to cramping. Insufficient hydration, both prior to and during the activity, will usually cause a decrease in blood volume, which will impair the delivery of electrolytes and nutrients to the muscles in question. Deficiencies in the minerals calcium, magnesium, and potassium, all of which play a significant role in the transmission of nervous system impulses to a muscle, as well as the regulation of heart rate, will also speed the formation of muscle cramps.

Caffeine, a substance commonly consumed by endurance athletes for both its stimulating as well as its glycogen-regulating qualities, is a contributor to muscle cramps by virtue of its diuretic (an increased urine output) properties. Caffeine will often speed the dehydration of the body.

In sports that require anaerobic energy production, lactic acid, a byproduct of the production of ATP, may cause an involuntary muscle contraction.

The initial treatment of a muscle cramp includes a gentle stretch of the affected area. If the cramp arises in competition, the athlete should not immediately attempt to return to full speed. The keys to the prevention of cramps are developing a high level of general fitness, regular and comprehensive stretching of the key muscle groups, and careful attention to nutrition practices, including carbohydrate, vitamin, and fluid levels.

Stomach cramps can be as disabling as muscle cramps, and as stomach problems most often arise in the pressure of competition, these cramps can have a significant negative impact on performance. For endurance athletes, stomach cramps often occur when the athlete consumes too much food or liquid during competition. When athletes eat too much food prior to an event, or when they experiment during a competition with a drink or an energy gel to which they are not accustomed, cramping may also result. In circumstances where the athlete consumes a great deal of water without having an adequate amount of sodium present in the system (a mineral lost through perspiration), a condition known as hyponatrania will arise, which results in excessive water in the stomach, which is not capable of being processed by the body.

When the athlete consumes an excessive or unaccustomed amount of dietary fiber in the one to two days leading up to an event, the athlete may experience stomach cramps that precede a bout of diarrhea.

Menstrual cramps will vary in intensity among female athletes. For some women, menstruation does not impact upon their training or competitive schedules. Other female athletes will often experience menstrual discomfort that ranges from a mild ache to a temporarily disabling condition, with pain radiating from the lower abdomen to the upper legs. Contributing factors to this condition include mineral level deficiencies, particularly calcium and magnesium, as well as with the predisposition of the athlete to debilitating menstrual cramps. The discomfort caused by these cramps is often reduced through the use of analgesics such as aspirin, heating pads placed on the abdomen, and gentle exercise.

see also Exercise and fluid replacement; Heat cramps; Sodium (salt) intake for athletes.