Athletic development specialists dedicated to the art and science of excellence in movement

Exploring Causes of Exercise Associated Muscle Cramps

Conventional wisdom on muscle cramps is that cramps are caused by some type of electrolyte imbalance.  However, several recent studies have cast doubt on the connection between hydration and cramping, with evidence pointing toward pacing, mechanics, and physical condition as factors behind camps.   These haven’t been identified as causative factors, but there is evidence of a link beyond hydration status.  We’re mostly interested in preventing cramps from starting, though hydration may indeed save us from an acute episode.       

Why does the electrolyte explanation persist?  Well, there hasn’t been any evidence to fully disprove it.  Electrolytes may indeed be at fault but for reasons different than we suspect.   Secondly, and perhaps most importantly, blaming an electrolyte imbalance is a more convenient way for us athletes to preserve confidence and self-dignity in light of poor training and racing tactics!  I have to admit, I have used this excuse for myself in the past and have at times relied on the conventional wisdom to explain cramps in others. 

When we go out too hard and muscles seize up, it’s mentally appealing to blame the calamity on some perceived uncontrollable force like hydration (even though it’s something fully within our control).  I don’t mind athletes playing victim to preserve confidence, but at some point it is necessary to confront the realities of what causes the problem.  In part, you don’t want to blame nutrition/hydration and discard a perfectly good plan that was never at fault.  Further, the discussion gets even murkier when "hardcore" athletes use the word “cramp” to describe an actual injury (tendonosis, tendonitis, muscle tearing, etc)!

Pacing and previous training are two key factors to consider.  Regarding pacing, if you go out too hard, bad things will happen at the end of the race.  The body will find a way to rebel no matter how well you eat and hydrate.  Sprint the first mile of a marathon and no magic potion of food or drink will save you.  It’s easy to say "I didn’t drink enough" or "didn’t drink the right stuff", but we also need to be honest if we overestimate our fitness level and start at an unsustainable pace. 

Previous training is another factor, particularly for ultra-distance events.  Note that some of the studies below focus on Ironman races.  One common omission from Ironman programs are rides that replicate conditions of the race.  Riding one hundred miles with three coffee breaks at a leisurely pace and drafting had different demands on the body than long rides in the aerobars, no stops, and no drafting.  Obviously not every ride should be like that (and there’s still a place for the leisurely long rides) but such rides are the proving ground for race day pacing strategies.

Schwellnus (2011) looked at Ironman athletes and found several factors associated with muscle cramping, which interestingly align with the scenario of going out too hard and blowing up.  Of the 43 athletes who cramped, they self-predicted faster race times than the non-cramping group and had faster cycling times, despite relatively close performance levels in previous races.  The faster cycling time is interesting coincides with the observation that Ironman run meltdowns are often preceded by overly aggressive bike (one great saying “there’s no such thing as a great bike followed by a bad run”).   In short, the athletes who pursued more aggressive race strategies were at greatest risk of cramping.  It would take more detailed analysis of each athlete’s pacing to see whether they actually overshot their fitness level with pacing, but there’s evidence pointing in that direction.

Schwellnus (2011) found similar factors associated with cramping in an ultramarathon (56km).  Runners in the cramping group and non-cramping group had similar marathon times, but the cramping group started out faster!  Prerace muscle damage and creatine kinase levels were higher among the cramping group.  If the body is worn down on the start line, hydration may be an ancillary consideration as the real problem is the training that put the athlete in a position of weakness (think rearranging the deck chairs on the Titanic!).   

Shang (2011) also looked at factors associated with muscle cramping in an Ironman triathlon:

·         Older

·         Taller

·         Heavier

·         Predicted a faster overall time during the Ironman Triathlon

·         Family history for EAMC

·         History of tendon and/or ligament injuries

·         Self-reported history of EAMC. 

Note there was no evidence to identify these as causes, but they were predictive factors that may help us refine the understanding of causes.  For instance, being taller and heavier is thought to make it harder for the body to cool itself, thus making an electrolyte imbalance more likely.  However, when you consider the entire picture, these factors are just two of the many associated with cramps.

A history of previous injuries is often overlooked, but deserves mention.  As with the Schwellnus (2011) ultramarathon study, there is evidence from Shang (2011) that poor movement quality is predictive of cramps.  Injuries and poor movement quality are very broad fields but rarely do athletes look to these areas (and the training that produced these conditions) as the underlying cause of cramping.  Hamstrings and calves are common cramping sites, but these are also muscles that get overused when other muscles don’t do their jobs!  When athletes start the race nursing injuries, how the body responds to duress is highly unpredictable.    

Wagner (2009) conducted a case study on an elite triathlete with history of cramping that tested the hypothesis of poor movement quality producing cramps in races.  EMG revealed poor muscle timing.  This athlete demonstrated weakness in the gluteus maximus, which coincided with the right hamstrings being activated excessively during terminal swing and the first half of the stance phase.  Strengthening and a movement reeducation program to activate his glutes and calm his hamstrings eliminated cramps in his subsequent races.


The whole point of this discussion is to address the actual problem.  If nutrition and/or hydration are not the problems, it means people are changing perfectly good nutrition/hydration plans in response to cramps.  Smarter training, controlled pacing, and improvements in movement quality are three overlooked areas that deserve attention to cure cramping problems.  


Wagner T, Behnia N, Ancheta WK, Shen R, Farrokhi S, Powers CM.  Strengthening and neuromuscular reeducation of the gluteus maximus in a triathlete with exercise-associated cramping of the hamstrings.  J Orthop Sports Phys Ther. 2010 Feb;40(2):112-9.

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.  Clin J Sport Med. 2011 May;21(3):204-10.

Schwellnus MP, Allie S, Derman W, Collins M.  Increased running speed and pre-race muscle damage as risk factors for exercise-associated muscle cramps in a 56 km ultra-marathon: a prospective cohort study.  Br J Sports Med. 2011 Nov;45(14):1132-6. Epub 2011 Mar 13.

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

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 Jun;45(8):650-6. Epub 2010 Dec 9.


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