As an athlete, it’s almost inevitable that you’ve experienced the intense, painful involuntary contraction of muscle fibers, better known as cramps. It’s just as likely that you heard, “Take magnesium to prevent cramps.” You or your teammates may even supplement with magnesium for this reason.
The belief is widespread. Yet, there is little to no strong evidence that magnesium prevents cramps. In fact, taking too much magnesium could actually be harmful. Let’s dive into the science.
Where Did This Belief Come From?
The idea that magnesium prevents cramps began in the mid-20th century. Researchers found that magnesium deficiency could cause involuntary muscle spasms, particularly in people with disorders like restless leg syndrome.
Because magnesium has a role in muscle function and neuromuscular transmission, it wasn’t a huge leap for researchers to assume magnesium could prevent cramps.
The theory took hold. Because exercise-associated muscle cramps (EAMCs) are common in athletes, it became especially prevalent in sports nutrition. Companies began marketing magnesium supplements as a way of preventing muscle cramps during exercise—despite having no proof.
Magnesium is often added to sports drinks to prevent cramps.
What Does the Science Say?
Cramps occur unpredictably and may involve multiple factors, making them difficult to study in a lab setting. As a result, there is surprisingly little research about magnesium and cramps. Further, much of the research is focused on pregnancy-related or nocturnal leg cramps—not exercise-associated muscle cramps.
Here is what key studies and reviews have found:
- A 2020 review found that magnesium supplementation is unlikely to treat or prevent muscle cramps in older adults, and there were not enough controlled studies on pregnancy-related and exercise-induced cramps.
- A 2017 study found that magnesium was no better than a placebo for alleviating nocturnal leg cramps.
- A 2021 meta-analysis found magnesium did not alleviate cramps in pregnant women compared to a control.
- A 2004 study of distance runners found that electrolyte concentration was not linked to cramps, and the athletes experiencing cramps actually had slightly higher post-race serum magnesium levels than those not experiencing cramps.
Arguments Against the Magnesium-Cramps Theory
Exercise physiologist Dr. Tim Podlogar points out that there’s no physiological mechanism by which magnesium would prevent cramps. During exercise, electrolyte concentrations inside cells actually increase, not decrease. This happens because dehydration causes cells to shrink, making electrolytes more concentrated, not deficient.
Further, stretching is one of the only proven ways to treat muscle cramps. If magnesium were to blame, stretching wouldn’t provide such an effective and immediate cure.
Stretching doesn’t affect magnesium levels.
What Really Causes Muscle Cramps?
Previously, researchers believed that EAMCs were caused by dehydration or electrolyte imbalance. However, research has largely ruled this out. Now, the prevailing theory is that cramps are caused by altered neuromuscular control.
The Altered Neuromuscular Control Theory
The Neuromuscular Theory suggests that fatigue disrupts the balance between excitatory and inhibitory signals in the nervous system, leading to cramps. Here’s how:
Normally, muscle tone is regulated by spinal reflexes involving two key receptors: muscle spindles, which promote contraction, and Golgi tendon organs (GTOs), which inhibit excessive muscle activity. These receptors work together to maintain neuromuscular control during movement.
However, when a muscle is overworked or fatigued, the inhibitory signals from the GTOs weaken, while excitatory signals from the muscle spindles increase, resulting in prolonged, uncontrolled contraction—a cramp.
Does the Theory Hold Up?
Compared to other theories, the neuromuscular theory has more data backing it up. One reason is because researchers are able to induce cramps with electrical stimuli, thus making it possible to test the neuromuscular theory.
Further, the neuromuscular theory is backed by the fact that stretching widely treats cramps. Stretching works by activating the Golgi tendon organs (GTOs), which send inhibitory signals to counteract the overactive excitatory signals.
The Role of Carbohydrates
Carbohydrates are the body’s primary source of fuel during exercise. Without enough carbohydrates, the muscles become fatigued. In theory, this could lead to the altered neuromuscular control which causes cramps.
Thus, low carbohydrate availability could be the underlying cause of muscle cramps in athletes. This theory is gaining traction in the sports nutrition world and is supported by many prominent experts, including Dr. Tim Podlogar.
Want to learn more? Read our Guide to Fueling.
Pro Fact: Cramps are also a common side effect of low carbohydrate diets like keto.
Why Does the Magnesium/Cramps Myth Persist?
Despite the lack of supporting research, the idea that magnesium prevents cramps persists. There are several reasons why this myth continues to hold weight:
- Anecdotal Evidence – Athletes who take magnesium and feel better may attribute their relief to the supplement, even if the improvement was due to other factors like the placebo effect or because their magnesium drink also contained carbohydrates.
- Marketing & Supplement Industry – Magnesium supplements are widely marketed for muscle health, and the line between fact and assumption has blurred over time.
- General Importance of Magnesium – Magnesium is an essential nutrient for muscle function and general health, which may lead people to believe it plays a direct role in cramp prevention, even though the evidence doesn't support this for EAMCs.
Magnesium May Have Other Athletic Benefits
While research doesn’t support magnesium for muscle cramps, there is some evidence that it can help athletic performance. For example, one review found that magnesium supplementation:
- Reduced muscle soreness
- Improved recovery and performance
- Induced a protective effect on muscle damage
However, this review also found that physically active individuals only need 10-20% more magnesium than the recommended dose. For most athletes, that means an additional ~40mg per day.
Yet, many sports supplements contain much more than this amount. For example, Gatorade’s Gatorlyte formula contains 105 mg of magnesium per serving, and athletes often consume multiple servings during exercise.
Nduranz fueling and hydration products contain magnesium, but only the amount actually lost through sweat during exercise.
The Risks of Consuming Too Much Magnesium
Not only is magnesium ineffective in preventing cramps, but taking too much could cause side effects.
A review of studies on magnesium for cramps found that magnesium supplementation caused gastrointestinal problems, such as diarrhea, in 37% of participants.
Considering that GI problems are very common in endurance athletes and one of the leading reasons for race drop-outs, this side effect could be detrimental to athletes.
Key Takeaway
The belief that magnesium prevents muscle cramps has been around for decades and is prevalent in the sports world, but modern research does not support this claim.
While magnesium may have some benefits, athletes should avoid consuming high amounts because of the risk of GI side effects. A better way to prevent muscle cramps is to ensure proper carbohydrate availability with loading and fueling.