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- Alex Hutchinson (@sweatscience)

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Another interesting study in the British Journal of Sports Medicine, posted online in December while I was away. It’s a prospective study that looked at 209 Ironman triathletes before and after a race, and tried to detect any differences between the 43 who developed muscle cramps and the 166 who didn’t. The major finding is that there was no significant difference in the levels of dehydration or electrolyte loss between the two groups, challenging the prevailing electrolyte-depletion hypothesis of cramps. The cramping group lost 2.8% body mass compared to 3.1% in the non-crampers; crampers’ sodium levels dropped 0.1% (+/- 1.9%), while the non-crampers increased 0.4% (+/- 2.6%).

The study comes from Martin Schwellnus’s group at the University of Cape Town. I wrote about Schwellnus’s theory of “altered neuromuscular control” for cramps last July, after returning from a visit to his lab. At the time, he was analyzing some data that he said suggested that crampers tend to be those who set faster time goals and start faster relative to their fitness, and who have trained more in the final week before the race (thus leaving their muscles fatigued). That suggested that realistic goal setting and an appropriate taper would minimize your risk.

The new study only bears part of that out. The three factors that predicted cramping were (1) faster predicted race time, (2) faster actual race time, and (3) previous history of cramping. Training volumes and paces for the final week before the race were more or less identical in the two groups, which means that in this group of athletes, a bad taper wasn’t to blame.

The fact that faster predicted and actual finishing time was associated with cramping is sort of bad news, because it doesn’t offer any simple solutions. The two groups were matched in terms of training history and personal best performances, so on the surface you’d expect them to aim for similar times. But it turns that those who aimed higher were more susceptible to cramps — and achieved better performances. So it seems (albeit from a single, isolated study) that cramping is just one of the many unavoidable risks associated with getting as close as possible to your limits, especially if you happen to have a (genetically determined?) history of cramping. You’d probably find a similar pattern if you measured the likelihood of dropping out or having a very big positive split: those who aim highest are most likely to blow up or drop out, but are also most likely to produce faster performances.

UPDATE Feb. 3: There’s quite a lively debate on this topic going on over at Slowtwitch. I just posted to address a couple of questions; my response is below: