Exercise-associated muscle cramps (EAMCs) are painful involuntary contractions of skeletal muscle during or after exercise. They are the most common heat-related illness (5) and affect recreationally active individuals (17) and competitive athletes alike (2,8,25). Despite their commonality, few well-designed research studies exist examining the cause, treatment, and prevention of EAMCs. As a result, numerous myths exist about EAMCs. My goal in this Medical Report will be to debunk some of these myths by examining the scientific evidence.
MYTH 1: EAMCs ARE CAUSED BY DEHYDRATION AND ELECTROLYTE LOSSES
This is the most popular myth believed by the medical community and general populace. For example, 92% of athletic trainers believe that dehydration or electrolyte imbalance causes EAMCs (24). Yet, few well-designed experimental studies actually support this myth. Rather, this misconception is supported by case studies (1,2) or observational studies (9,23). In addition to the low strength of evidence (Levels 3 and 4, Oxford Centre for Evidence Based Medicine), all of these studies examined athletes who did not actually experience EAMCs when the studies were conducted (1,2,9,23).
Several observations also argue against this myth. First, static stretching quickly relieves cramping (3,20,24). If dehydration caused EAMCs, stretching should have no effect because no fluids or electrolytes are added to the body with this treatment. Second, athletes with EAMCs often have similar body mass losses (11,19,20,25), blood electrolyte concentrations (19,25), and blood and plasma volumes (11,20) as noncramping athletes. Third, cramp-prone athletes often drink similar, if not more, fluid than athletes without a history of EAMCs (9,23). Fourth, even when sport drink ingestion matched sweat loss, EAMCs still occurred 70% of the time (10). Fifth, dehydration affects the whole body, yet it is often the working muscles (e.g., calves, hamstrings) that develop EAMCs. If EAMCs were caused by dehydration or electrolyte imbalance, we would observe random muscles cramping. Finally, in two well-designed experimental trials, cramp risk was unchanged when fatigue was minimized and subjects were dehydrated (4,15).
If dehydration caused exercise-associated muscle cramping, stretching should have no effect because no fluids or electrolytes are added to the body with this treatment.
MYTH 2: SPORT DRINKS CAN PREVENT EAMCs BY REPLACING THE ELECTROLYTES LOST DURING EXERCISE
Sport drinks contain electrolytes (e.g., sodium, potassium) but not in enough quantities to replenish completely what is lost during exercise. For example, crampers can lose 2.7 g/h of sodium via sweating (2). If these crampers exercised for 2.5 hours (e.g., a typical football practice), 6.75 g of sodium would need to be replaced. If the athletes consumed a typical sport drink containing 0.44 g/L of sodium, the athletes would need to drink 15.3 L (4 gallons) to replace their sodium losses fully! Drinking this much fluid is dangerous. In August 2014, two high school American football players died of exercise-associated hyponatremic encephalopathy (a.k.a., water intoxication). In one case, it was estimated that the athlete drank 4 gallons (15.1 L) of water and sport drinks because he suffered from EAMCs (22). The deaths of these athletes may have been prevented had they followed the guideline of drinking when thirsty (7). Therefore, electrolytes must be replaced at meals rather than by drinking sport drinks.
MYTH 3: STATIC STRETCHING WILL HELP PREVENT EAMCs
Undoubtedly, stretching is the most effective way to relieve an active cramp (3,6). In fact, muscles cannot cramp if they are not allowed to shorten (3). However, several field studies have failed to show a link between stretching habits and EAMC occurrence (19,21,26). Moreover, we showed in a laboratory study (13) that 3 minutes of static stretching did not increase calf inhibition. This means that it is unlikely that stretching before exercise would prevent the overexcitation in the nervous system thought to contribute to EAMC genesis (18). Whether stretching may help prevent EAMCs through other means (e.g., improving range of motion) is still unknown.
Undoubtedly, stretching is the most effective way to relieve an active cramp (3,6). In fact, muscles cannot cramp if they are not allowed to shorten (3). However, several field studies have failed to show a link between stretching habits and exercise-associated muscle cramping occurrence (19,21,26).
MYTH 4: THERE IS NO WAY TO PREDICT WHO WILL GET EAMCs
It is true that EAMCs are spontaneous and, at times, unpredictable. However, a prior history of EAMCs or a family history of EAMCs seems to be a good predictor of cramp risk (14,21,26). This suggests that there may be a genetic component to EAMCs. Thus, asking athletes if they, or their immediate family, have ever had EAMCs can be a useful question to identify people at risk of EAMCs. These individuals can then be targeted with possible interventions like neuromuscular reeducation, which may help prevent future EAMCs (27).
MYTH 5: BANANAS CAN RELIEVE EAMCs BY INCREASING BLOOD POTASSIUM
This is a popular myth propagated by the belief that EAMCs are caused by electrolyte losses. Unfortunately, it takes at least 30 minutes to see an increase in new potassium ions in the blood after banana ingestion (12). Thus, eating bananas is unlikely to help an athlete with an active EAMC because of the delay in blood potassium changes. In addition, there is no evidence that eating bananas effectively prevents or treats EAMCs.
The cause of EAMCs is likely multifactorial and caused by changes in the neuromuscular system (16,18). This multifactorial nature may explain why so many myths exist regarding treatment and prevention of EAMCs. Our care of athletes prone to EAMCs must be evidence based and extend beyond cookie-cutter recommendations (e.g., drink more fluids containing electrolytes). Clinicians should study their cramp-prone athletes to identify the unique risk factors that make them prone to EAMCs. For example, the athlete could keep a “cramp journal” and document the events that preceded EAMCs (e.g., diet, hydration, exercise duration and intensity, sleep, environmental conditions). Once trends in risk factors emerge, clinicians should target those factors with treatments and prevention strategies.
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