Exercise-associated muscle cramping (EAMC) in Ironman triathletes
Exercise-associated muscle cramping (EAMC) is a common condition of spontaneous, painful skeletal muscle spasms that occur in exercising muscles during exercise or in the immediate post-exercise period. There is a high prevalence in endurance athletes, including ultra-distance triathletes. The exact cause for this condition has not been defined but various hypotheses have been proposed. Over the last decade the ""fatigue hypothesis"" has received most of the support in the scientific literature. Evidence from animal experiments, clinical studies on endurance athletes and situational information, suggest that neuromuscular fatigue may precede the increased neuromuscular excitability leading to EAMC. The objective of this research study was to identify factors associated with EAMC in endurance triathletes in an attempt to further elucidate the aetiology. Triathletes competing in the 2006 South African lronman triathlon were recruited as subjects in a prospective cohort study. A total of 44 triathletes made up the cramping group and 166 the non-cramping group. A detailed questionnaire, including information on training, personal best performances and a cramping history was completed by both groups of triathletes. Full clinical data was also collected from both groups. This included pre-and post race body weights, and pre- and post-race serum electrolyte concentrations. The main findings of the study were that the two independent risk factors for EAMC in these triathletes were a faster overall race time (and cycling time), and a past history of cramping (in the last 10 races). Results showed that EAMC was correlated with faster overall and cycle section times. The athletes who had experienced cramps in this event not only achieved taster race times but also predicted faster times, despite similarly matched preparation and performance histories as those who did not cramp. A higher intensity of racing would thus be required by these athletes, predisposing them to premature fatigue. The results thus agree with the ""fatigue hypothesis"" as an aetiological mechanism for EAMC. This study also showed no correlation between EAMC and changes in hydration status or changes in serum electrolyte concentration. This study thus adds to the evidence against disturbances in hydration and electrolyte balance as causes for cramping in exercise and further focuses attention on neuromuscular fatigue as a possible primary factor.
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