Virtually every athlete remembers suffering a muscle cramp at some point. Months of thorough preparation can be ruined by this sudden and painful response of the body. In fact, a study involving 82 marathon runners found that one in five experienced a cramp (1). Similar results were observed in another study involving 210 triathletes competing in an Ironman (2). And if you haven’t experienced one yet, it might just be a matter of time; a survey of more than 1,000 marathoners showed that nearly 40% had experienced a cramp at least once in their life (3). But what causes cramps, and what can we do to avoid them?
Cramps: What Causes Them?
The exact causes that trigger muscle cramps remain largely unknown. Traditionally, dehydration has been blamed, especially since almost a century ago many cases of cramps were reported among soldiers or workers exposed to heat and dehydration, such as miners or construction workers. Importantly, researchers found that when these individuals drank only water, the incidence of cramps did not change, whereas it decreased when they drank water with added mineral salts (4). In other words, it could be hyponatremia (a drop in salt concentration), and not just dehydration, that causes cramps.
However, it’s important to note that hyponatremia is just one of many potential causes. In fact, many of our readers likely remember suffering a cramp even when it wasn’t hot or they weren’t dehydrated. This has led to the development of other theories, one of the main ones involving the nervous system. It has been observed that excessive nervous excitation —sending more signals than necessary to the muscles or failing to properly inhibit them (for example, when working in very short range of motion)— could cause a cramp. Similarly, excessive muscle fatigue may also interfere with the correct contraction-relaxation process, promoting the onset of cramps.
This can be seen in many sports. For example, during a marathon, most cramps occur in the final stages of the race (after km 30), when muscle fatigue is high, regardless of hydration status (3). Additionally, it has been observed that the risk of cramps increases the less trained a person is or the higher the intensity of competition compared to usual training levels, which also supports the fatigue theory (3).
Sports Drinks and Cramps
Although cramps are often associated with mineral salt-based sports drinks, the possible role of carbohydrates is often overlooked. We’ve previously discussed the benefits of carbohydrates for performance. In fact, carbohydrates have been shown to delay fatigue during prolonged exercise, which is what we now refer to as “durability.” Therefore, considering the role of muscle fatigue in cramps, it’s not surprising that carbohydrate intake could help prevent cramps.
In a study involving university students, researchers developed a protocol to induce local fatigue in the calf muscles under hot and humid conditions, in order to maximize the chance of cramp occurrence (5). The researchers found that the number of participants experiencing cramps was about the same, regardless of whether they drank a beverage containing electrolytes and 56 grams of carbohydrates or drank nothing at all. However, the time to cramp onset was more than doubled when the carbohydrate-electrolyte drink was consumed (15 minutes vs. 37 minutes without any drink) (5).
Thus, in this case, a sports drink containing both carbohydrates and electrolytes proved effective in delaying the negative effects of cramps. Unfortunately, we cannot determine whether the benefits came from the electrolytes or the carbohydrates. However, the fact that there was minimal dehydration even in the group that didn’t hydrate (only a 1% loss of body weight) suggests that dehydration did not play a major role.
Conclusions
Cramps have a multifactorial origin, potentially caused by dehydration and hyponatremia (loss of electrolytes), but also by excessive muscle fatigue or hyperactivation of the nervous system. Therefore, relying on a single preventive method is counterproductive. However, the use of sports drinks with both electrolytes and carbohydrates may help mitigate the negative effects of dehydration and fatigue, thereby reducing the incidence of cramps or at least delaying their onset.
AUTHOR
Pedro Valenzuela
Researcher at the Physiology Unit of the University of Alcalá and at the Performance Control Unit of the Sports Medicine Center (AEPSAD, CAR of Madrid).
Website: www.fissac.com
References
- Maughan RJ. Exercise-induced muscle cramp: A prospective biochemical study in marathon runners. J Sports Sci. 1986;4(1):31–4.
- 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.
- Schwellnus MS, Noakes TD. Risk Factors for Exercise Associated Muscle Cramping (EAMC) in Marathon Runners. Med Sci Sport Exerc. 1996;28(5):167.
- Talbott BYJH, Michelsen J. HEAT CRAMPS. A CLINICAL AND CHEMICAL STUDY. J Clin Invest. 1933;12(9):533–49.
- Jung AP, Bishop PA, Al-Nawwas A, Dale RB. Influence of hydration and electrolyte supplementation on incidence and time to onset of exercise-associated muscle cramps. J Athl Train. 2005;40(2):71–5.
