What causes leg cramps, and How can you prevent them? Muscle cramps can be very painful and disrupt muscle function. Additionally, cramps can be quite annoying, especially in the middle of the night! In this article, you will learn what muscle cramps are, what types and causes exist, and how to treat them.

What causes leg cramps and why – The basics

Muscle cramps are painful disruptions of muscle function. The involuntary contractions of the muscles can last for several seconds or even significantly longer. Cramps can occur in generally healthy individuals. There are different types and causes of muscle cramps that can be distinguished (1-6). These include exercise-induced muscle cramps, nocturnal cramps (especially in older people), and cramps during pregnancy (1, 3, 6). The cramp contractions are associated with repeated firing of motor unit action potentials. This myoelectric activity has been referred to as “cramp discharge.” Cramps can occur in patients with lower motor neuron diseases, neuropathies, metabolic disorders, and acute extracellular volume deficiency (5). The epidemiology in the healthy adult population is about 50-60%, with an increase in incidence with age and during exercise (2). In an otherwise healthy neuromuscular system (i.e., the nerve-muscle connections), the following factors can play a role in the occurrence of cramps (1, 3, 4):

• Insufficient fluid supply
• Electrolyte shift/electrolyte losses (e.g., when you sweat more, you also lose electrolytes, especially sodium, but also other electrolytes such as magnesium or chloride)
• Overloading of the muscular system (e.g., intensive and long-lasting use of the muscles)

However, the dehydration hypothesis and the electrolyte depletion hypothesis show inconsistent scientific evidence (2). In addition, medications and overdoses of medications can also trigger muscle cramps. Therefore, identifying the cause is an important first step in treating cramps. However, pathological conditions such as neurological disorders, thyroid dysfunction, and vascular diseases can also lead to muscle cramp dysfunction (1, 3).

What causes leg cramps?

Muscle cramps are likely of neurogenic origin (from the nerves). An earlier hypothesis suggested that cramps result from the hyperexcitability of motor neurons (central or spinal origin hypothesis) (5). Although the origin of cramps is not fully understood, much suggests that cramps result from spontaneous discharges of motor nerves or abnormal excitation of the distal or remote branches of motor axons (peripheral or axonal origin hypothesis) (5, 6). Nonetheless, the cause of muscle cramps appears to be multifactorial. Possible causes can be summarized in 3 groups of causes (2):

1. Caused by pathological factors (such as metabolic disorders, diabetes, neuropathy)
2. Idiopathic nocturnal cramps are painful episodes of muscle cramps that occur during sleep without a clear origin
3. Exercise-Associated Muscle Cramps (EAMC), are muscle cramps that occur during or after exercise

Muscle cramps after intensive or extensive physical activity usually occur in the stressed muscles during or immediately after exertion. In contrast, cramps associated with pregnancy or advancing age tend to occur in the legs or feet during periods of rest (6).

What should you clarify?

If you are currently suffering from muscle cramps (especially if they occur regularly), it makes sense to ask yourself the following questions:

• Have I exerted myself recently (before the onset of muscle cramps) (sports, work, leisure)?

→ If yes, what was the stress? (How long? How intense? Was the stress unusual? What were the outside temperatures? Did I sweat a lot? Did I drink enough before, during, and after the stress? Did I consume enough electrolytes before, during, and after the stress (sodium, magnesium…))?

• Have I eaten or drunk differently lately?

→ If yes, what was different? (Did I eat a low-salt diet? Did I eat a high-salt diet? Did I eat a low-iodine diet for a long time? Did I drink less?)

• Am I taking dietary supplements? If so, which ones?
• Am I taking medication? If so, which ones?

If cramps of unexplained origin occur frequently (i.e., not due to high stress or similar), it may make sense to investigate the cause further. A doctor can help with this.

How to prevent load-related muscle cramps?

The following points can help prevent exercise-induced muscle cramps (fully scientifically proven findings on the prevention of muscle cramps do not yet seem to exist, but the following points could possibly have a positive effect on exercise-induced muscle cramps):

• Reduction of load (volume, intensity)
• Regular flexibility training (esp. stretching)
• Plyometric exercises (e.g., jumps) can improve the elastic properties of the muscle-tendon-fascia unit and neuromuscular coordination
• In case of high sweat losses, you should “top up” with sufficient fluids and electrolytes, e.g., supply of common salt (sodium chloride) or isotonic drinks as needed

Muscle cramps and the role of magnesium

There is evidence that magnesium supplements are unlikely to help prevent muscle cramps, especially in older adults. However, the research findings for pregnant women with leg cramps are contradictory and unclear. Until 2020, no randomized controlled trial (RCT) had been conducted to investigate the effect of magnesium on exercise-induced muscle cramps or disease-related muscle cramps (6). Therefore, it is currently not scientifically advisable to praise or condemn the importance of magnesium in exercise-induced muscle cramps (own statement). To better understand the role of magnesium in preventing or treating muscle cramps in pregnant women and people with exercise- or disease-related cramps, high-quality research is necessary. Future studies should measure the frequency of cramps during treatment with magnesium and summarize the results to draw a clear conclusion (6).

If you want to learn more about the anatomy and function of the muscles, feel free to check out other articles on my blog, such as the anatomy of the Adductors. I appreciate your feedback and questions in the comments. You may also find interesting videos on fitness & co on my YouTube channel.

References

1. Diener, H. C., & Westphal, K. (2013). Differenzialdiagnose und Therapie von Muskelkrämpfen (Crampi). MMW-Fortschritte der Medizin, 155(5), 83-86.

2. Giuriato, G., Pedrinolla, A., Schena, F., & Venturelli, M. (2018). Muscle cramps: A comparison of the two-leading hypothesis. Journal of electromyography and kinesiology, 41, 89-95.

3. Hollmann, W., & Strüder, H. K. (2009). Sportmedizin: Grundlagen für körperliche Aktivität, Training und Präventivmedizin; mit 91 Tabellen. Schattauer Verlag.

4. Mihaylova, V., & Jung, H. H. (2017). Muskelkrämpfe – die neurologische Perspektive. Praxis.

5. Minetto, M. A., Holobar, A., Botter, A., & Farina, D. (2013). Origin and development of muscle cramps. Exercise and Sport Sciences Reviews, 41(1), 3-10.

6. Garrison, S. R., Korownyk, C. S., Kolber, M. R., Allan, G. M., Musini, V. M., Sekhon, R. K., & Dugré, N. (2020). Magnesium for skeletal muscle cramps. Cochrane Database of Systematic Reviews, (9).