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Cramps in Swimming….What is the Cause?

by ZwemZa on November 15th, 2014

swimmingcrampCramping (exercise associated muscle cramps; EAMC) is gaining traction since LeBron James exited a recent NBA Finals game. Cramps occur often in swimmers, commonly in the foot and calf. It is common folklore that dehydration and a lack of electrolytes cause cramping, but scientific literature has been dismissing this notion for years (Schwellnus 2009). If hydration and electrolytes are the scapegoats of camps, what is the cause?


Fatigue is a complex phenomenon having origins in the muscle (peripheral fatigue) as well as the brain and spinal cord (central fatigue). Most often cramping occurs in times of fatigue, the end of a set, directly after a hard set, or early in the season. The caused of cramping is poorly understood, but central and peripheral overload in the muscle during fatigue likely results in a cramp. This overload “short circuits”, altering the neuromuscular control of the muscle.

Now, some may say how do we know dehydration or electrolyte loss during fatigue isn’t the cause? Well, as a Physical Therapist, I’ve worked with many patients who cramp during a first set of an exercise. This often occurs when a patient is activating a muscle which hasn’t fired in years! This lack of conditioning increases it’s likelihood of cramping. Also, previous work by Schwellnus (2010) notes dehydration and sodium (electrolyte) changes during an Ironman do not increase cramps. Instead, running speed and a previous history of cramping are the cause.

Braulick (2013) attempted to induce cramping in a group of hydrated and dehydrated participants. This study found dehydration did not increase cramp risk.

Once again, increased fatigue = increases cramp risk, but is this the only factor?

History of Cramps

Another contributor of cramping is genetics. A cross-sectional survey study highlighted family history of EAMC as a factor that is associated with a past history of EAMC in 1300 marathon runners (Manjra 2006). This association was later confirmed in a case-control study of 433 Ironman triathletes where the frequency of a positive family history of EAMC was significantly more common in triathletes with a past history of EAMC (36.6%) when compared to those with no history of EAMC (16.4%) (Shang 2011).

O’Connell (2013) had two hundred and sixty-eight Caucasian participants were recruited from the 2006 and 2007 226 km South African Ironman triathlon (n=211) or the 2009 and 2011 56 km Two Oceans ultra-marathon (n=57) for this study. One hundred and eighteen participants reported a history of EAMC within the last 12 months prior to the event (EAMC group), while 150 reported no history of a previous (lifelong) EAMC (NON group).

This study found: The COL5A1 rs12722 (C/T) variant was associated with self-reported EAMC during the 12 months prior to participating in either the 2006 and 2007 South African Ironman triathlons or the 2009 and 2011 Two Oceans ultra-marathons. Specifically, the CC genotype was significantly over-represented in participants with no self-reported history of previous (lifelong) EAMC (CC genotype; 21.8%) when compared to participants that reported a past history of EAMC within 12 months prior to the event (CC genotype; 11.1%). Multivariate regression analysis also revealed the COL5A1 rs12722 TC and TT genotypes as positive contributors to risk of past history of EAMC. This was the first study to identify a genetic variant as a potential marker for a past history of EAMC. These results suggest that changes to type V collagen containing connective tissue may directly and/or indirectly modulate the risk of a past history of EAMC, however further investigation is required.

Fatigue + Genetic History = Cramping … But What to Do With a Cramp

If someone is having a cramp, the individual should stop exercising and rest. Assuming the individual does not suffer from any medical conditions that may be causing the cramping, passive stretching is the best form of treatment (Miller 2010). Anecdotally, self myofascial releases are also helpful for alleviating a cramp.

Cramp Prevention…We Don’t Know Much!
Individuals prone to muscle cramping should avoid exercising in hot or humid conditions, exercise at lower intensities and for shorter durations, stretch affected muscles regularly and ensure that they have adequate nutritional intake. The individual may also consult a clinician about possible underlying medical conditions that may result in muscle cramping (Schwellnus 2008).


  1. Shang G, Collins M, Schwellnus MP. Factors associated with a self-reported history of exercise-associated muscle cramps in ironman triathletes: a case-control study. Clinical Journal of Sport Medicine. 2011;21:204-210. 
  2. Schwellnus M. Increased running speed and previous cramps rather than dehydration or serum sodium changes predict exercise-associated muscle cramping: a prospective cohort study in 2010 Ironman Triathletes. BR J Sports Med. Dec 2010.
  3. Schwellnus M. Cause of exercise associated muscle cramps (EAMC)–altered neuromuscular control, dehydration or electrolyte depletion? Br J Sports Med. Jun 2009;43(6):401-408.
  4. O’Connell K, Posthumus M, Schwellnus MP, Collins M.Collagen genes and exercise-associated muscle cramping. Clin J Sport Med. 2013 Jan;23(1):64-9. doi: 10.1097/JSM.0b013e3182686aa7.
  5. Braulick KW, Miller KC, Albrecht JM, Tucker JM, Deal JE. Significant and serious dehydration does not affect skeletal muscle cramp threshold frequency. Br J Sports Med. 2013 Jul;47(11):710-4. doi: 10.1136/bjsports-2012-091501. Epub 2012 Dec 6.
  6. Manjra SI, Schwellnus MP, Noakes TD. Risk factors for exercise associated muscle cramping (EAMC) in marathon runners. Medicine and Science in Sports and Exercise. 1996;28:S167. 
  7. Miller KC, Stone MS, Huxel KC et al. Exercise-associated muscle cramps: causes, treatment, and prevention. Sports Health. 2010;2:279-283.

Gary Mullen

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