Muscle cramps during exercise

Muscle cramps during exercise are relatively common and have been investigated for decades but remain a mystery. Scientists have identified potential risk factors, causes and solutions but evidence is not very solid.

Exercise-associated muscle cramps

Also known as EAMC, these are cramps that happen during or immediately after exercise (1, 2). Muscle cramps occur in a wide range of athletes participating in a variety of disciplines. These are most commonly reported in endurance-type sports and team sports (1) although this could be due to research bias.

EMAC are usually a minor inconvenience but they can vary in intensity and duration, with a very small percentage of the population experiencing severe cramping (1). This, of course, can affect training and competition.

Can cramps be prevented?

Cramps are hard to predict as they normally occur spontaneously. Unfortunately, this means EMAC are difficult to study and hard to prevent. Scientists sometimes use electrical impulses to stimulate muscles and get them to cramp, but this is not 100% reliable not an accurate representation of what actually happens during exercise (1).

What causes muscle cramps during exercise?

In short: we don’t know. However, the main 2 hypotheses are:

1. Hydration and electrolyte balance

Old evidence in the literature pointed to dehydration through sweating as a potential cause for cramps (1). It has been postulated that the dilution of electrolyte concentration due to sweating too much and/or drinking too much water may lead to more cramping. However, studies looking at electrolyte changes in blood have failed to establish a solid correlation between the concentration of electrolytes in blood and EAMC. Having said that, it is possible that the electrolyte concentration in blood does not reflect what happens at the exercising muscle level (1, 2).

When using electricity to induce cramps, scientist have concluded that hydrating with an electrolyte-containing beverage reduces susceptibility to EAMC in individuals who have experience dehydration via sweat (1).

2. Altered neuromuscular control

This second hypotheses indicates that because passive stretching of the muscle relieves cramping, there must be motor neurons implicated in the process. In particular, it seems that the spinal control of motor neuron function is altered during EAMC (1).

This is why scientists use electricity to activate a muscle while in its shortened state to induce cramping. The threshold frequency of the electric stimulus needed to induce cramping seems to be lower in athletes who normally experience cramping (1).

Risk factors for muscle cramps during exercise

Potential risk factors that have been associated with EAMC are:

• Temperature: there are more reported cases when exercising in hot weather (1, 2) but cramps do happen in lower temperatures (1)
• Intensity: evidence from endurance and team sports suggest cramping occurs when intensity of training/competition is higher (1)
• Duration: evidence from marathon runners suggests the duration of the event is also directly correlated with risk of cramping (1)
• Fatigue: muscle fatigue is another commonly cited risk factor for EAMC (1)
• Individual factors: older age, higher body mass index (BMI) and a family history of cramping also increase the risk of EAMC. Athletes who have experienced cramping in the past have additional risk factors: some chronic diseases, cancer, allergies, medications and having experienced injuries. Other sources have indicated that a lower BMI is also a risk factor (1), which leads me to believe that the relationship is U-shaped.
• Stretching: lack of stretching has been cited as a potential risk factor (1)

How to prevent and treat muscle cramps

• Electrolytes (1), which target hypothesis #1 (see What causes muscle cramps during exercise?)
• Passive stretching (1), which target hypothesis # 2 (see What causes muscle cramps during exercise?)
• Pickle juice, thought to be effective in reducing duration of cramps if taken very shortly after the initiation of the cramp (1). Here is a link for Pickle Juice, an Australian product targeted to athletes.
• Quinine, the component that gives tonic water its bitterness, may reduce the incidence and/or intensity of cramps when taken in daily doses of 200-500 mg. The effect may be increased by the addition of theophylline, a drug used for the treatment of respiratory disease (1)

Summary and recommendations

Science has identified potential risk factors and possible causes of exercise-associated muscle cramps. However, none of them stands out on its own, suggesting a variety of factors are involved. Athletes who normally experience muscle cramping should aim to maintain hydration and electrolyte balance and perform passive stretching on exercising muscles to lower the incidence, severity and/or duration of EAMC. In addition, consider trialling a pickle juice or quinine supplement with the guidance of a sports dietitian.

References

1. Maughan RJ, Shirreffs SM. Muscle Cramping During Exercise: Causes, Solutions, and Questions Remaining. Sport Med [Internet]. 2019;49(2):115–24. Available from: https://doi.org/10.1007/s40279-019-01162-1
2. Lau WY, Kato H, Nosaka K. Effect of oral rehydration solution versus spring water intake during exercise in the heat on muscle cramp susceptibility of young men. J Int Soc Sports Nutr [Internet]. 2021;18(1):22. Available from: https://doi.org/10.1186/s12970-021-00414-8

[Photo by sporlab on Unsplash]

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