Muscle cramps can be associated with metabolic, endocrine, and neurological disorders. However, many healthy, athletic individuals also suffer from recurrent muscle cramping brought on by exercise. Muscle cramps that occur during or following exercise, in the absence of disease, are termed Exercise-Associated Muscle Cramps (EAMC). Most recreational and competitive athletes have experienced EAMC, with corresponding negative effects on performance. Currently there is not a certain cause. There are only theories.
Two Theories of EAMC
- Dehydration-Electrolyte Imbalance Theory: The dehydration-electrolyte imbalance theory states that EAMC is the result of fluid and electrolyte depletion, which results in the sensitization of nerve terminals. Exercise in hot/humid environments exacerbates EAMC due to increased fluid loss.
- Neuromuscular Theory: The neuromuscular theory states that EAMC occurs in a contracting muscle due to an imbalance between excitatory muscle spindle impulses and inhibitory Golgi Tendon Organ (GTO) impulses. Muscle spindles are specialized receptors in muscle that monitor velocity and length changes. They respond to a quick stretch by reflexively contracting. GTOs respond to tension, and inhibit muscle contraction by inhibiting the action of the muscle spindle. An imbalance between the two can lead to EAMC.
- There is evidence supporting both of these theories.
Prevention of EAMC
- Stay hydrated: The amount of fluid you consume should allow for less than a 2% reduction in body weight during exercise. Weighing yourself before and after exercise is a simple way of monitoring for adequate fluid intake. For athlete’s susceptible to EAMC, it is recommended to add 0.3 to 0.7 g/L of salt to fluids, to replace lost electrolytes. Many sports drinks do not contain sufficient levels of electrolytes to replace that which is lost. Keep in mind that it takes at least 15 minutes for ingested fluid to be absorbed into the blood stream. Ingesting about 1 liter of water or a sports drink one hour before exercising is typically sufficient to ensure adequate availability of fluid, electrolytes, and nutrients. Eating a balanced diet is also very important.
- Train appropriately: Both plyometric training and endurance training can help to delay neuromuscular fatigue and prevent an imbalance between muscle spindle and GTO activity. Plyometric training utilizes stored elastic energy in muscle to produce increased force during contraction. It incorporates dynamic activities, and consists of an eccentric (lengthening) muscle contraction immediately followed by a concentric (shortening) muscle contraction. Plyometric training can increase the speed of contraction, as well as the force output. For more information on plyometric training, click here! Endurance training can increase time to fatigue, and potentially eliminate EAMC by increasing the efficiency of the muscle spindles and GTOs.
The recommended treatment for acute EAMC is moderate stretching of the affected muscle. Contracting the antagonist (opposite muscle) can help by reflexively inhibiting the affected muscle. For example, flexing the quadriceps will cause a reflexive relaxation of the hamstrings. Fluid replacement is important as well. In some cases, intravenous fluid replacement and medications have been used. If EAMC persist it is important to rule out other potential causes, such as diabetes or thyroid disease.