Exercise Associated Muscle Cramps (EAMC) are something that I’ve suffered from badly in the past to a point where they have left me a hobbling mess during a race and basically incapable of running. With the triathlon season having kicked off I thought I’d review this common but still poorly understood ailment that unfortunately still has a lack of good quality scientific evidence to guide management. EAMC affects a large amount of athletes in all sports and this article covers our current understanding of this complex condition.
The first theory put forward for the cause of EAMC over 50 years ago was based on dehydration or abnormal serum electrolyte concentrations (decreased sodium, potassium, magnesium, chloride and calcium). Unfortunately we hung our hat on this theory for a long time but it fails to hold any weight when we know that EAMC is localised to skeletal muscles used during exercise (ie. quads, calves, hamstrings) and experimentally induced dehydration causes generalised skeletal muscle cramping. Four prospective cohort studies have shown no relationship between sodium loss and EAMC in marathon runners and triathletes.
The current and most plausible cause for EAMC is the altered neuromuscular control theory and the underlying cause is muscle fatigue. Factors that will contribute to muscle fatigue are exercising at a higher than normal intensity or for a longer duration, decreased muscle energy (carbohydrate depletion), environmental conditions (unacclimatised heat), inadequate conditioning (not pushing yourself enough in your hard sessions to simulate race conditions) and a genetic predisposition. The key is to get your head around this part- fatigued muscles show an increased excitatory afferent input (increased electrical stimulation to the muscle from the spinal cord) and a decreased inhibitory afferent output (we have stretch receptor cells in our tendons called Golgi Tendon Organs or GTO’s that feed back information to our spinal cord telling our muscles to reduce their contraction). This represents altered neuromuscular control and results in increased alpha motor neuron activity and results in the muscle cramping. If I haven’t lost you by now then well done! To put it more simply- if we keep using at a high intensity an already fatigued muscle (increased alpha motor neuron drive) that has lost the ability to feedback and decrease the drive (GTO’s not working so well) then we will eventually cramp.
So what do we do about it? Acute cramps are relieved by stretching hence further backing up the GTO theory however prevention is always better than cure. Avoiding extreme muscle fatigue is key which can be hard to do in the heat of a race when you are pushing yourself harder then you usually would. Maintaining a good energy supply is essential so have a good understanding of how many grams of carbs you will need during the race or event. The second is essentially to train harder, or race easier. If you have big disparity between the intensity or duration of your hard training sessions and your race pace then you will be more likely to reach muscle fatigue. Pushing yourself to your race pace or above in your hard training sessions (one to two a week maximum) is a key way to avoid fatigue and cramping. This can take months and years if your are competing at a high level so a long term approach and patience is key. Alternatively reassessing and being realistic about your race pace will help avoid EAMC so discussing with a coach or other experienced athletes is advisable.
I hope this helps clear up an old misconception about a common exercise associated ailment and provides a more current theory on its cause. It isn’t exhaustive and is an overview so if you have any further queries please feel free to contact me on campbell@squareonephysio.com.au
