If you've ever had muscle spasms or muscle cramps, you know they can be extremely painful. In some cases, a muscle may spasm so forcefully that it results in a bruise on the skin.
Most muscle spasms and cramps are involuntary contractions of a muscle. A serious muscle spasm doesn't release on its own and requires manual stretching to help relax and lengthen the shortened muscle.
Spasms and cramps can be mild or extremely painful. While they can happen to any skeletal muscle, they are most common in the legs and feet and muscles that cross two joints (the calf muscle, for example).
Cramps can involve part of a muscle or all the muscles in a group. The most commonly affected muscle groups include:1
Back of lower leg/calf (gastrocnemius)
Back of thigh (hamstrings)
Front of thigh (quadriceps)
Feet, hands, arms, abdomen
Muscle cramps range in intensity from a slight twitch or tic to severe pain. A cramped muscle can feel rock-hard and last a few seconds to several minutes or longer.
It is not uncommon for cramps to ease up and then return several times before they go away entirely.
Causes of Muscle Cramps
The exact cause of muscle cramps is still unknown, but the theories most commonly cited include:2
Altered neuromuscular control
Doing a new activity
Other factors that have been associated with muscle cramps include exercising in extreme heat.1
Because athletes are more likely to get cramps in the preseason, near the end of (or the night after) intense or prolonged exercise, some feel that a lack of conditioning results in cramps.
Neuromuscular Control and Cramps
While all these theories are being studied, researchers are finding more evidence that the "altered neuromuscular control" hypothesis is the principal pathophysiological mechanism the leads to exercise-associated muscle cramping (EAMC).
Altered neuromuscular control is often related to muscle fatigue and results in a disruption of muscle coordination and control.
According to a review of the literature conducted by Martin Schwellnus from the University of Cape Town, the evidence supporting both the "electrolyte depletion" and "dehydration" hypotheses as the cause of muscle cramps is not convincing.3
He reviewed the available literature supporting these theories and found mostly anecdotal clinical observations and one small case-control study with only 10 subjects. He also found another four clinical prospective cohort studies that clearly did not support the "electrolyte depletion" and "dehydration" hypotheses as for the cause of muscle cramps.
In his review, Schwellnus concludes that the "electrolyte depletion" and "dehydration" hypotheses do not offer plausible pathophysiological mechanisms with supporting scientific evidence that could adequately explain the clinical presentation and management of exercise-associated muscle cramping.
He goes on to write:
"Scientific evidence for the 'altered neuromuscular control' hypothesis is based on evidence from research studies in human models of muscle cramping, epidemiological studies in cramping athletes, and animal experimental data. Whilst it is clear that further evidence to support the 'altered neuromuscular control' hypothesis is also required, research data are accumulating that support this as the principal pathophysiological mechanism for the aetiology of exercise-associated muscle cramping (EAMC)."
Schwellnus published a study in 2011 of 210 triathletes found that dehydration and altered serum electrolyte balance were not causes for exercise-associated muscle cramps. Instead, cramps were more frequent in those who ran faster than expected, suggesting that more intense exercise could be the cause risk factor.4
Muscle Cramp Treatment and Prevention
Cramps usually go away on their own without treatment and until we learn the exact cause of muscle cramps, it will be difficult to say with any confidence how to prevent them. However, these tips are most recommended by experts and athletes alike:1
Stop the activity that caused the cramp.
Gently stretch and massage the cramping muscle.
Hold the joint in a stretched position until the cramp stops.
Improve fitness and avoid muscle fatigue.
Stretch regularly after exercise.
Warm-up before exercise.
Stretch the calf muscle in a standing lunge with both feet pointed forward by straightening the rear leg.
Stretch the hamstring muscle by sitting with one leg folded in and the other straight out, foot upright and toes and ankle relaxed, leaning forward slightly, and touching the foot of straightened leg.
Stretch the quadriceps muscle while standing by holding the top of your foot with the opposite hand and gently pull heel toward buttocks.
Most muscle cramps are not serious. If your muscle cramps are severe, frequent, constant, or of concern, see your doctor.
1. The American Academy of Orthopaedic Surgeons. Muscle cramps. Updated June 2017.
2. Bordoni B, Sugumar K, Varacallo M. Muscle cramps. StatPearls. Updated June 22, 2019.
3. Schwellnus MP. Cause of exercise-associated muscle cramps (EAMC)--altered neuromuscular control, dehydration or electrolyte depletion?. Br J Sports Med. 2009;43(6):401-8. doi:10.1136/bjsm.2008.050401
4. Schwellnus MP, Drew N, Collins M. Increased running speed and previous cramps rather than dehydration or serum sodium changes predict exercise-associated muscle cramping: a prospective cohort study in 210 Ironman triathletes. Br J Sports Med. 2011;45(8):650-6. doi:10.1136/bjsm.2010.078535