Serum electrolyte concentrations and hydration status are not associated with exercise associated muscle cramping (EAMC) in distance runners.
OBJECTIVE
To determine whether acute exercise associated muscle cramping (EAMC) in distance runners is related to changes in serum electrolyte concentrations and hydration status.


METHODS
A cohort of 72 runners participating in an ultra-distance road race was followed up for the development of EAMC. All subjects were weighed before and immediately after the race. Blood samples were taken before the race, immediately after the race, and 60 minutes after the race. Blood samples were analysed for glucose, protein, sodium, potassium, calcium, and magnesium concentrations, as well as serum osmolality, haemoglobin, and packed cell volume. Runners who suffered from acute EAMC during the race formed the cramp group (cramp, n = 21), while runners with no history of EAMC during the race formed the control group (control, n = 22).


RESULTS
There were no significant differences between the two groups for pre-race or post-race body weight, per cent change in body weight, blood volume, plasma volume, or red cell volume. The immediate post-race serum sodium concentration was significantly lower (p = 0.004) in the cramp group (mean (SD), 139.8 (3.1) mmol/l) than in the control group (142.3 (2.1) mmol/l). The immediate post-race serum magnesium concentration was significantly higher (p = 0.03) in the cramp group (0.73 (0.06) mmol/l) than in the control group (0.67 (0.08) mmol/l).


CONCLUSIONS
There are no clinically significant alterations in serum electrolyte concentrations and there is no alteration in hydration status in runners with EAMC participating in an ultra-distance race.
University of Cape Town, UCT/MRC Research Unit for Exercise Science and Sports Medicine, Department of Human Biology, Faculty of Health Sciences, University of Cape Town, Boundary Road, Newlands 7700, South Africa. mschwell@sports.uct.ac.za
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Schwellnus
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Nicol
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Laubscher
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Noakes
D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D001790:Blood Physiological Phenomena; D015331:Cohort Studies; D004573:Electrolytes / Q000097:blood*; D015444:Exercise / Q000502:physiology*; D006454:Hemoglobins / Q000032:analysis; D006801:Humans; D009120:Muscle Cramp / Q000097:blood / Q000209:etiology* / Q000503:physiopathology; D011446:Prospective Studies; D012420:Running / Q000502:physiology*; D014882:Water-Electrolyte Balance / Q000502:physiology*
D001786:Blood Glucose; D004573:Electrolytes; D006454:Hemoglobins