title: 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.
abstract: BACKGROUND
  Despite the high prevalence of exercise-associated muscle cramping (EAMC) in endurance athletes, the aetiology and risk factors for this condition are not fully understood.
  
  
  OBJECTIVE
  The aim of this prospective cohort study was to identify risk factors associated with EAMC in endurance triathletes.
  
  
  METHODS
  210 triathletes competing in an Ironman triathlon were recruited. Prior to the race, subjects completed a detailed validated questionnaire and blood samples were taken for serum electrolytes. Immediately before the race, pre-race body weight was obtained. Body weight and blood samples for serum electrolyte concentrations were obtained immediately after the race. Clinical data on EAMC experienced during or immediately after the race were also collected.
  
  
  RESULTS
  43 triathletes reported EAMC (cramping group) and were compared with the 166 who did not report EAMC (non-cramping group). There were no significant differences between groups in any pre-race-post-race serum electrolyte concentrations and body weight changes. The development of EAMC was associated with faster predicted race times and faster actual race times, despite similarly matched preparation and performance histories in subjects from both groups. A regression analysis identified faster overall race time (and cycling time) and a history of cramping (in the last 10 races) as the only two independent risk factors for EAMC.
  
  
  CONCLUSIONS
  The results from this study add to the evidence that dehydration and altered serum electrolyte balance are not causes for EAMC. Rather, endurance runners competing at a fast pace, which suggests that they exercise at a high intensity, are at risk for EAMC.
authors.affiliation: UCT/MRC Research Unit for Exercise Science and Sports Medicine, Department of Human Biology, University of Cape Town, Cape Town, South Africa. martin.schwellnus@uct.ac.za
authors.forename: Martin P
authors.initials: MP
authors.lastname: Schwellnus
authors.forename: Nichola
authors.initials: N
authors.lastname: Drew
authors.forename: Malcolm
authors.initials: M
authors.lastname: Collins
mesh_terms: D001642:Bicycling / Q000502:physiology; D001835:Body Weight; D003681:Dehydration / Q000097:blood / Q000150:complications*; D004326:Drinking; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009120:Muscle Cramp / Q000097:blood / Q000209:etiology*; D052580:Muscle Stretching Exercises; D011446:Prospective Studies; D012307:Risk Factors; D012420:Running / Q000502:physiology*; D012964:Sodium / Q000097:blood; D013550:Swimming / Q000502:physiology; D014882:Water-Electrolyte Balance / Q000502:physiology
chemical_list: D012964:Sodium