Aetiology of Muscular Cramps in Marathon Runners

Review of article outlining Current State of Knowledge for Muscle Cramps after Long Distance Running

Martin P. Schwellnus; Sports Med 2007; 37 (4-5): 364-367

This is not a novel article as such, but more a review of other articles, and therefore is short on data. So, take it for what it is.

EAMC is the commonly used term, or, "exercise associated muscular contraction", which the author expands and adds qualifications to become "a painful spasmodic involuntary contraction of skeletal muscle that occurs during or after exercise."

Two of the more commonly hypothesised aetiological causes of "muscle cramps" have been "electrolyte imbalance" and "dehydration". He explains why electrolyte imbalance, although implicated in severe enough cases, with generalised muscle spasm, is unlikely to be the cause in localised muscle cramps of the type seen in sports or distance running. Likewise, he describes a
number of studies that seemingly disprove dehydration as a causative agent.

The rest of the article puts forth the position that "muscle fatigue" is the chief cause of EAMC. It is quite technical so I will spare the details. Suffice to say, lack of details notwithstanding, I find this hypothesis more credible than others, and bears out my own personal experience.

My editorial;
I have had my share of muscle cramps in my younger days from other sports like soccer and tennis. Invariably, they occurred after prolonged sessions in either sport. When you are young you think you are invincible and will push well past your limit. To date, have not had any cramps while training or racing long distance running. This of course is occurring only recently for me, in my more prudent, middle aged state, when I rarely push so hard outside my envelope. I did, during my very first marathon, feel a cramp coming on in my right quad at about 35km, a distance I have not reached before in training. Having been the "beneficiary" of previous cramps, I backed off the speed and ended up run-walk the rest of the way.

I believe, hydration, electrolyte top-up and so forth as useful insofar as they put off the point when fatigue sets in. But at the end of the day, it would appear that your exertions on the day, in relation to your training levels, will determine how quickly and badly you fatigue, and hence how prone you will be to cramping.