Cramp

A cramp is a sudden, involuntary muscle contraction or over-shortening; while generally temporary and non-damaging, they can cause mild-to-excruciating pain, and a paralysis-like immobility of the affected muscle(s). Onset is usually sudden, and it resolves on its own over a period of several seconds, minutes, or hours. Cramps may occur in a skeletal muscle or smooth muscle. Skeletal muscle cramps may be caused by muscle fatigue or a lack of electrolytes (e.g., low sodium, low potassium, or low magnesium, although the evidence has been mixed). Cramps of smooth muscle may be due to menstruation or gastroenteritis.

Differential diagnosis

Causes of cramping include^[1] hyperflexion, hypoxia, exposure to large changes in temperature, dehydration, or low blood salt. Muscle cramps can also be a symptom or complication of pregnancy; kidney disease; thyroid disease; hypokalemia, hypomagnesemia, or hypocalcaemia (as conditions); restless legs syndrome; varicose veins;^[2] and multiple sclerosis.^[3]

Electrolyte disturbance may cause cramping and muscle tetany, particularly hypokalemia and hypocalcaemia. This disturbance arises as the body loses large amounts of interstitial fluid through sweat. This interstitial fluid comprises mostly water and salt (sodium chloride). The loss of osmotically-active particles outside of muscle cells leads to a disturbance of the osmotic balance and therefore shrinking of muscle cells, as these contain more osmotically-active particles. This causes the calcium pump between the muscle sarcoplasm and sarcoplasmic reticulum to "short circuit"; the calcium ions remain bound to the troponin, continuing muscle contraction.

As early as 1965, researchers observed that leg cramps and restless legs syndrome can result from excess insulin, sometimes called hyperinsulinemia.^[4]

Skeletal muscle cramps

Skeletal muscles can be voluntarily controlled, under normal circumstances. Skeletal muscles that cramp the most often are the calves, thighs, and arches of the foot, and are sometimes called a "Charley horse" or a "corky". Such cramping is associated with strenuous physical activity and can be intensely painful; however, they can even occur while inactive and relaxed. Around 40% of people who experience skeletal cramps are likely to endure extreme muscle pain, and may be unable to use the entire limb that contains the "locked-up" muscle group. It may take up to seven days for the muscle to return to a pain-free state.

Nocturnal leg cramps

Nocturnal leg cramps are involuntary muscle contractions that occur in the calves, soles of the feet, or other muscles in the body during the night or (less commonly) while resting.

The duration of nocturnal leg cramps is variable, with cramps lasting anywhere from a few seconds to several minutes. Muscle soreness may remain after the cramp itself ends. These cramps are more common in older people.^[5] They happen quite frequently in teenagers and in some people while exercising at night. The precise cause of these cramps is unclear. Potential contributing factors include dehydration, low levels of certain minerals (magnesium, potassium, calcium, and sodium, although the evidence has been mixed),^[6][7][8] and reduced blood flow through muscles attendant in prolonged sitting or lying down. Nocturnal leg cramps (almost exclusively calf cramps) are considered "normal" during the late stages of pregnancy. They can, however, vary in intensity from mild to extremely painful.

A lactic acid buildup around muscles can trigger cramps; however, these happen during anaerobic respiration when a person is exercising or engaging in an activity where the heartbeat speeds up. Medical conditions associated with leg cramps are cardiovascular disease, hemodialysis, cirrhosis, pregnancy, and lumbar canal stenosis. Differential diagnoses include restless legs syndrome, claudication, myositis, peripheral neuropathy. All of these can be differentiated through careful history and physical examination.^[8]

Gentle stretching and massage, putting some pressure on the affected leg by walking or standing, or taking a warm bath or shower may help to end the cramp.^[9] If the cramp is in the calf muscle, pulling the big toe gently backwards will stretch the muscle and, in some cases, cause almost immediate relief. There is limited evidence supporting the use of magnesium, calcium channel blockers, carisoprodol, and vitamin B12.^[8]

Quinine is no longer recommended for treatment of nocturnal leg cramps due to potential fatal hypersensitivity reactions and thrombocytopenia. Arrhythmias, cinchonism, hemolytic uremic syndrome can also occur at higher dosages.^[8]

Smooth muscle cramps

Smooth muscle contractions may be symptomatic of endometriosis or other health problems. Menstrual cramps may also occur both before and during a menstrual cycle.

Iatrogenic causes

Various medications may cause nocturnal leg cramps:^[8][10]

• Diuretics, especially potassium sparing
• Intravenous (IV) iron sucrose
• Conjugated estrogens
• Teriparatide
• Naproxen
• Raloxifene
• Long acting adrenergic beta-agonists (LABAs)
• Hydroxymethylglutaryl-coenzyme A reductase inhibitors (HMG-CoA inhibitors or statins)

Besides being painful, a nocturnal leg cramp can cause much distress and anxiety.^[11] Statins may sometimes cause myalgia and cramps among other possible side effects. Raloxifene (Evista) is a medication associated with a high incidence of leg cramps. Additional factors, which increase the probability for these side effects, are physical exercise, age, female gender, history of cramps, and hypothyroidism. Up to 80% of athletes using statins suffer significant adverse muscular effects, including cramps;^[12] the rate appears to be approximately 10–25% in a typical statin-using population.^[13][14] In some cases, adverse effects disappear after switching to a different statin; however, they should not be ignored if they persist, as they can, in rare cases, develop into more serious problems. Coenzyme Q10 supplementation can be helpful to avoid some statin-related adverse effects, but currently there is not enough evidence to prove the effectiveness in avoiding myopathy or myalgia.^[15]

Pathophysiology

Skeletal muscles work as antagonistic pairs. Contracting one skeletal muscle requires the relaxation of the opposing muscle in the pair. Cramps can occur when muscles are unable to relax properly due to myosin fibers not fully detaching from actin filaments. In skeletal muscle, adenosine triphosphate (ATP) must attach to the myosin heads for them to disassociate from the actin and allow relaxation; the absence of ATP in sufficient quantities means that the myosin heads remains attached to actin. An attempt to force a muscle cramped in this way to extend (by contracting the opposing muscle) can tear muscle tissue and worsen the pain. The muscle must be allowed to recover (resynthesize ATP), before the myosin fibres can detach and allow the muscle to relax.

Treatment

Stretching, massage and drinking plenty of fluid, such as water, may be helpful in treating simple muscle cramps.^[16] With exertional heat cramps due to electrolyte abnormalities (primarily sodium loss and not calcium, magnesium, and potassium), appropriate fluids and sufficient salt improves symptoms.^[17]

Medication

Quinine is likely to be effective; however, due to side effects, its use should only be considered if other treatments have failed.^[18] Vitamin B complex, naftidrofuryl, lidocaine, and calcium channel blockers may be effective for muscle cramps.^[18] Research has also shown that pickle "juice" can be an effective remedy based on its high sodium and electrolyte content.^[19] Cyclobenzaprine (Flexeril) has proven effective in preventing muscle cramps, although data suggests that effectiveness decreases when taken for more than several weeks.

Prevention

Adequate conditioning, stretching, mental preparation, hydration, and electrolyte balance are likely helpful in preventing muscle cramps.^[16]

References

External links

• What are Cramps?
• Cramps at Patient UK
• Muscle Cramps (of Skeletal Muscles)

Diving medicine, physiology, physics and environment
Diving medicine:	Injuries and Disorders Pressure Oxygen Deep water blackout Hyperoxia Oxygen toxicity Shallow water blackout Inert gases Atrial septal defect Avascular necrosis Decompression sickness Dysbaric osteonecrosis High-pressure nervous syndrome Hydrogen narcosis Isobaric counterdiffusion Nitrogen narcosis Taravana Uncontrolled decompression Carbon dioxide Hypercapnia Aerosinusitis Air embolism Alternobaric vertigo Barodontalgia Barostriction Barotrauma Compression arthralgia Decompression illness Dental barotrauma Dysbarism Ear clearing Frenzel maneuver Valsalva maneuver Immersion Asphyxia Drowning Hypothermia Hypoxia (medical) Immersion diuresis Instinctive drowning response Salt water aspiration syndrome Swimming-induced pulmonary edema List of signs and symptoms of diving disorders Cramps Diving disorders Seasickness Treatments Diving chamber Diving medicine Hyperbaric medicine Hyperbaric treatment schedules In-water recompression Oxygen therapy
Diving physiology	Artificial gills (human) Blood–air barrier Blood shift CO₂ retention Cold shock response Decompression (diving) Decompression theory Gas exchange History of decompression research and development Lipid Mammalian diving reflex Maximum operating depth Metabolism Normocapnia Oxygen window in technical diving Perfusion Physiological response to water immersion Pulmonary circulation Respiratory exchange ratio Respiratory quotient Systemic circulation Tissue (biology)
Diving physics	Ambient pressure Amontons' law Anti fog Archimedes' principle Atmospheric pressure Boyle's law Breathing performance of regulators Buoyancy Charles' law Combined gas law Dalton's law Diffusion Diving physics Force Gay-Lussac's law Henry's law Hydrophobe Hydrostatic pressure Ideal gas law Molecular diffusion Neutral buoyancy Oxygen fraction Partial pressure Permeation Pressure Psychrometric constant Snell's law Solubility Solution Supersaturation Surface tension Surfactant Torricellian chamber Underwater vision Weight
Diving environment	Algal bloom Breaking wave Current (ocean) Current (stream) Ekman transport Halocline Longshore current Rip current Stratification Surf Surge (wave action) Thermocline Tides Turbidity Undertow (water waves) Upwelling
Researchers in diving medicine, physiology and physics	Arthur J. Bachrach Albert R. Behnke Paul Bert George F. Bond Sir Robert Boyle Albert A. Bühlmann John R Clarke William Paul Fife John Scott Haldane Robert William Hamilton, Jr. Leonard Erskine Hill Felix Hoppe-Seyler Christian J. Lambertsen Simon Mitchell Charles Momsen John Rawlins (Royal Navy officer) Charles Wesley Shilling Edward D. Thalmann Jules Triger
Diving medical research organisations	Aerospace Medical Association Divers Alert Network Diving Diseases Research Centre Fitness to dive List of diving hazards and precautions National Board of Diving and Hyperbaric Medical Technology Naval Submarine Medical Research Laboratory Royal Australian Navy School of Underwater Medicine Rubicon Foundation South Pacific Underwater Medicine Society Undersea and Hyperbaric Medical Society United States Navy Experimental Diving Unit
Categories: Diving medicine Underwater diving physiology Underwater diving physics Physical oceanography Glossary Portal