Serum electrolytes in Ironman triathletes with exercise-associated muscle cramping.
OBJECTIVE
To compare serum electrolyte concentrations of cramping and control Ironman triathletes.


METHODS
Triathletes suffering from acute exercise-associated muscle cramping (EAMC) after the 2000 South African Ironman Triathlon formed the cramping group (CR, N = 11). Non-cramping triathletes matched for race finishing time and body mass formed the control group (CON, N = 9). All subjects were weighed at race start and immediately post-race. Blood samples were drawn from both groups during recovery for the analysis of serum magnesium, glucose, sodium, potassium and chloride concentrations. Hemoglobin concentration and hematocrit were also measured. Surface electromyography (EMG) (mV) was recorded from a non-cramping control muscle (triceps) and the most severely cramping lower limb muscle of the CR group. EMG was recorded at the beginning of every minute for a 10-min period during recovery.


RESULTS
There were no significant differences between the groups for body mass or percent body mass loss during the race. Post-race sodium concentration was significantly lower (P = 0.01) in the CR group than the CON group (140 +/- 2 vs 143 +/- 3 mmol.L) but was within the normal clinical range of post-race serum sodium concentrations. There were no significant differences between the two groups for post-race serum electrolytes, glucose, hemoglobin concentrations or hematocrit. Surface EMG (mV) was significantly higher (P < 0.05) in the cramping muscles than the control muscle of the CR group at 0, 3, 4, and 5 min of the 10-min recording period.


CONCLUSIONS
Acute EAMC in ironman triathletes is not associated with a greater percent body mass loss or clinically significant differences in serum electrolyte concentrations. The increased EMG activity of cramping muscles may reflect increased neuromuscular activity.
Sulzer
Nicole U
NU
UCT/MRC Research Unit for Exercise Science and Sports Medicine, Department of Human Biology, Faculty of Health Sciences, University of Cape Town, South Africa.
Schwellnus
Martin P
MP
Noakes
Timothy D
TD
D000328:Adult; D016022:Case-Control Studies; D004573:Electrolytes / Q000097:blood*; D004576:Electromyography; D006801:Humans; D009120:Muscle Cramp / Q000097:blood / Q000503:physiopathology*; D005082:Physical Exertion / Q000502:physiology*; D013019:South Africa; D013177:Sports
D004573:Electrolytes