A muscle cramp is a sudden, involuntary, painful contraction of a muscle. They are usually self-extinguishing within seconds to minutes. 1
Cramps can sometimes be the symptom of a nervous system or metabolic disorder, however, they often occur in healthy subjects with no history of such disorders.1 The latter are what we may call “benign cramps'' and these will be the focus of this article. Benign cramps often occur during sleep, pregnancy, and strenuous physical exercise.
Muscle cramping during or immediately after physical exercise was first reported more than 100 yr ago in miners working in hot and humid conditions. Dehydration (and/or electrolyte depletion) often is given as an explanation for muscle cramps occurring in workers and athletes, although this claim is not supported by scientific evidence.1
The main risk factors for exercise-associated muscle cramps include family history of cramping, previous occurrence of cramps during or after exercise, increased exercise intensity and duration, and inadequate conditioning for the activity (too hot, too cold etc).1
What causes muscle cramps?
The cause of muscle cramps is still not well understood. There is some evidence to suggest that they result from changes in motor neuron excitability. We can think of this like a minor glitch in the electrical signaling between the brain and muscle. Cramps are probably due to a confluence of unique intrinsic and extrinsic factors that are difficult to clearly identify.2
Exercise associated muscle cramps are more common the more fatigued a person is, for instance towards the end of a long running race. The factors underlying the variability in people’s cramp propensity, and why different muscles are more or less likely to cramp, are still unclear.
What can you do when a cramp occurs?
Most people will get relief from a painful cramp by performing a gentle stretch of the affected muscle. The effect is often not instantaneous, but develops over several seconds. If no active relief measures are undertaken the muscle will spontaneously gradually relax, but perhaps only after several minutes. For some hours, or even days afterwar the cramped portion of muscle tissue may be tender and painful.3
Does stretching help prevent cramps, or reduce their intensity?
A systematic review was done in 2021 to look at what therapies can help to prevent muscle cramps.4 A systematic review is where a team of researchers critically appraise all relevant research on a topic, analyse the data and formulate evidence based recommendations.
The results of this review concluded that the inconsistency and the low overall quality of available data makes it difficult to state anything definitive about cramp treatment. There was some low quality evidence that calf and hamstring stretching may reduce the severity of night-time lower limb muscle cramps in people aged 55 years and older, but the effect on cramp frequency is uncertain.
Long story short, there isn’t enough evidence to say whether stretching has a significant effect on preventing or mitigating cramps. As always, more research is needed. But at this stage, we would not routinely recommend stretching as a treatment for cramps.
Does heat or cold affect cramps?
Environmental heat or cold are probably both precipitating factors that can make cramps more likely to occur.3 However, there isn't a lot of quality data on this topic.
There is some evidence that local heat (such as a hot water bottle or a heated electric blanket) can be helpful in preventing nocturnal muscle cramps in the legs.3
Are cramps caused by dehydration? Or by low electrolytes - such as Magnesium, Sodium or Potassium?
Although the idea has been around for a long time, we simply don't have any evidence to say that cramps result from dehydration.
Likewise, when it comes to electrolytes, there isn't any compelling evidence that they can have a positive or negative effect on cramps.
So far the research in this area has concluded that:
As always, more research is needed. But at this stage, we would not recommend supplementing electrolytes as a treatment for cramps.
The relationship between physical activity and nocturnal cramps
Nocturnal leg cramps are a frequent disorder, which have a negative impact on quality of life, particularly among people over 60 years old. Lifestyle factors such as alcohol consumption have been shown to be associated with nocturnal leg cramps.
One recent study7 aimed to explore the association between nocturnal leg cramps and a sedentary lifestyle. The study recruited 272 participants aged 60 years or older. There was a strong association found, with the results showing that a sedentary person was 2.38 times more likely to experience nocturnal leg cramps than a physically active person. Just another great reason to exercise more!