Cramp - the emerging science

We’ve all had cramp at one time or another, yet it remains one of the most confusing and controversial subjects in sports science. Not only are we still unclear on how to cure or prevent it, but arguments still exist regarding its cause.

Exercise Associated Muscle Cramp can be defined as a painful, spasmodic and involuntary contraction of skeletal muscle that occurs during or immediately after exercise (1). We’ve all had them, and nobody likes them. So what can we do to stop them?

Historically, cramps have been studied in the heat, particularly in coal miners and the military. This led to them first being referred to as heat cramps; associated with hot temperatures, excessive sweating and sodium loss.

More recent studies have shown that cramp can also occur in low temperatures (2,3); that blood electrolyte levels (such as sodium, potassium, magnesium and calcium) are similar in crampers and non-crampers (4), and that dehydration does not increase the risk of cramping (5). This evidence suggests that the previous theories of “electrolyte depletion” and “dehydration” may not hold true, has led scientists to explore other causes of cramp.

Recent evidence is painting a picture (which is by no means complete) of “altered neuromuscular control” potentially causing cramp; or that cramp is a neurological response to muscle fatigue.

These studies have teased out the factors that increase muscular fatigue while controling other possible contributors, and found increased incidence of cramp (6).

These factors causing musclular fatigue that were associated with cramp include higher exercise intensity, longer exercise duration, reduced muscle energy stores, inadequate conditioning for the activity, and hot and/or humid environment.

An interesting example of this was a study done in South African Ironmen where athletes who cramped during the race were compared to athletes who did not. One significant finding was that when athletes with similarly matched training and performance histories were compared, an independent risk factor for cramp was faster racing time (increased exercise intensity) and increased muscle fatigue. The authors concluded that the athletes who tried to go faster than their peers who had done the same training more likely to cramp.

Other lab-based research shows that cramping can reliably be induced in subjects through voluntary sustained maximal muscle contraction (7); that episodes of cramping are electrically active (suggesting neuro-muscular mechanisms) (7); and that cramp can be caused by repetitive electrical stimulation of the nerves supplying the motor input to muscle (8).

Aspects that require further research are the role of previous muscle injury (which increases cramp), and family and personal history of cramping (suggesting a genetic predisposition) (2).

While not yet proven in the literature, it looks to me that this neuro-muscular response to increased muscular fatigue that causes the cessation of exercise (cramp), is related to the central governor theory. This theory states that the brain has a series of conscious and unconscious mechanisms (of which cramp is one) which prevent us from over-reaching (and thus increasing our internal temperature to a catastrophic level) during exercise.

 

  • So what does this mean for you? As an athlete (weekend warrior or not) we can use this knowledge to create the following strategies to help us prevent cramp:
  • Don’t rely on a magic drink to prevent cramp. It won’t (although the placebo effect is still a powerful ally).
  • Prepare well for your event - do the right training to ensure you are well conditioned!
  • Complete some training sessions at the intensity you expect to compete at.
  • Compete at a sensible intensity (by all means push yourself, but be realistic relative to your preparation).
  • Don’t make sudden changes in speed or direction if it can be helped.
  • Ensure you are well nourished and well fuelled heading into any training or competition. See a sports dietitian if you want specialist advice.
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What are your thoughts? It's certainly hard to get your head around the fact that salt sticks, electrolyte drinks, and staying well hydrated may not benefit you in terms of cramp, and you can bet your bottom dollar the sports drinks companies will still push these products and theories. An interesting topic indeed... Comment below the references.

    • 1) Schwellnus MP, Derman EW, Noakes TD. Aetiology of skeletal muscle ‘cramps’ during exercise: a novel hypothesis. J Sports Sci 1997;15:277–85.

      2) Armstrong LE, Casa DJ, Millard-Stafford M, et al. Exertional Heat Illness during Training and Competition. ACSM Position stand. Med Sci Sports Exerc 2007;39:556–72.

      3) Laird RH. Medical care at ultraendurance triathlons. Med Sci Sports Exerc 1989;21:S222–S225

      4) Schwellnus M, Nicol J, Laubscher R, et al. Serum electrolyte concentrations and hydration status are not associated with exercise associated muscle cramping (EAMC) in distance runners. Br J Sports Med 2004;38:488–92.

      5) Braulick K, Miller K, Albrecht J, Tucker J, Deal J. Significant and serious dehydration does not affect skeletal muscle cramp threshold frequency. Br J Sports Med 2013;47:710–714.

      6) Schwellnus M. Cause of Exercise Associated Muscle Cramps (EAMC) — altered neuromuscular control, dehydration or electrolyte depletion? Br J Sports Med 2009;43:401–408

      7) Norris FH, Gasteiger EL, Chatfield PO. An electromyographic study of induced and spontaneous muscle cramps. EEG Clin Neurophysiol 1957;9:139–47.

      8) . Minetto MA, Botter A, Ravenni R, et al. Reliability of a novel neurostimulation method to study involuntary muscle phenomena. Muscle Nerve 2008;37:90–100.