What are the causes of muscle cramps in athletes?

The research and the so whats?

Muscle cramps during endurance and team sport exercise are common, even in the fittest masters athletes. One of the international experts in the area, Michael Bergeron, an American sport scientist, recently reviewed the limited research in the area of muscle cramping. He concluded that as the research evidence grows, it’s becoming increasingly clear that there are two distinct and different categories of exercise-associated muscle cramps.

calf muscleFirstly, overloading muscles too hard and the associated fatigue can bring on muscle cramping locally in the overworked muscle fibres. These cramps can be treated effectively with stretching and massaging the affected muscle(s), icing the muscle group, or by lowering the exercise intensity. Prevention of these types of cramps  measures include reducing training and competition intensity and duration, as well as improving both the athlete’s fitness level and flexibility through regular individualized progressive fitness and stretching programs. Adjustments to equipment configuration and selection (e.g. bicycle seat and handle position, shoes), technique, and relaxation techniques may also help.

In contrast, the second type of cramping is commonly seen during endurance or team sports when training or competing in hot and humid conditions. These types of cramps appear due to extensive sweating and the associated sodium deficit caused by insufficient intake sodium intake to offset sweat sodium losses. This can lead to muscle cramping, even when there is little or no muscle overload and fatigue. Recovery and maintenance of water and sodium balance by drinking sodium-containing fluids (sports drinks) or intravenous salt solutions are the proven effective strategy for resolving and preventing exercise-associated muscle cramps that are bought on by extensive sweating and a sodium deficit.

Dr Bergeron suggests that at the first sign of muscle twitches or heat cramps, a prompt drink of a high-salt solution (e.g. 0.5 L of a carbohydrate-electrolyte drink, with 3.0 g of salt added and thoroughly mixed, consumed all at once or over 5-10 min) may help. Massaging and applying ice to the affected area can assist in relaxing the muscles and relieving some of the discomfort while waiting for the ingested fluid and salt to be absorbed into the blood, although the effects of the salt solution are usually seen in just a few minutes. Additional lower-sodium fluids such as sports drinks should then be consumed at regular intervals. After the training or competition session, any remaining body water and electrolyte deficits need to be replaced with a particular emphasis on salt intake. Intravenous drips with normal or saline may be required if muscle cramping is severe or accompanied by a more serious clinical condition such as hyponatremia (low blood sodium levels). Potassium-rich supplements or foods or other mineral supplements such as calcium or magnesium are not indicated and typically will not provide any relief of muscle cramp symptoms.

Big sweaters are often unable to avoid large water and electrolyte deficits during activity, particularly if doing same-day or day-after-day sessions, even if they drink commercial carbohydrate-electrolyte drinks and add salt to meals. Particularly when there is a short recovery time between sessions (sometimes only 1 hr between matches in tournament tennis or team sports),  these athletes (especially if prone to heat cramps) must focus on consuming a high-salt solution at regular intervals along with ingesting additional fluid and electrolytes (emphasizing salt intake). Profuse sweating and a salt ‘tracks’ on the skin or clothing and other signs and symptoms of dehydration (e.g. thirst, light headaches or nausea) further implicate the presence of a significant water or sodium deficit.

Salt tablets can be effective in treating exertional heat cramps, as long as they are taken with plenty of water (e.g. for 1 gm of NaCl per tablet, three crushed and dissolved tablets to 1 litre of water). For the athlete attempting to reverse a pattern of heat cramping, it is often not necessary to increase fluid intake. In fact, sometimes it’s essential to decrease fluid intake during and after activity for those who are over-drinking (especially those who are drinking too much low- or no-sodium fluid such as water). The key is to increase sodium intake to more closely match individual sweat sodium losses.

Photo from: Jonathon Cohen

Bergeron, M. (2008). Muscle cramps during exercise — is it fatigue or electrolyte deficit? Current Sports Medicine Reports. 7(4): S50-S55.