Blood Electrolytes in NFL Players while Experiencing EAMC compared to when they are not Cramping after Similar Practice Conditions

Abstract

Exercise associated muscle cramps (EAMC) are common in NFL players during preseason but they are difficult to study experimentally therefore the etiology is not well understood. Electrolyte disturbances and dehydration have been implicated in EAMC. PURPOSE: To analyze blood samples taken from NFL players at the time of EAMC with those taken from the same players after similar practices when they are not cramping and make comparisons in blood electrolytes and percent dehydration (%Dehy). METHODS: During the first two weeks of preseason training camp blood samples were drawn from 12 NFL players (age = 26.4 ± 2.9 y, height = 187 ± 7 cm, mass = 109 ± 19 kg, BSA = 2.34 ± 0.2 m2 and BSA/mass = 216 ± 17 cm2 kg-1) when they were experiencing EAMC prior to receiving intravenous fluids. Blood was also obtained from these players after a similar practice in similar environmental conditions when they did not have EMAC. Blood samples were immediately analyzed for sodium (Na+), potassium (K+) and chloride (C1-) by ion-selective electrode. Body mass was recorded before and after the same practices when blood was drawn to determine %Dehy. Additional data obtained at the time of EAMC but not used for comparisons were hematocrit (Hct), hemoglobin (Hb), lactate and serum osmolality (freezing point depression). RESULTS: There were no differences in blood Na+ (139.6 ± 2.0 mmol/l) or K+ (4.65 ± 0.8 mmol/l) when players had EAMC compared to when they did not (139 ±1.0 mmol/l and 4.88 ± 0.4 mmol/l) respectively. Blood Cl- was significantly lower when players had EAMC (98.2 ± 2.1, range = 94 to101 mmol/l) compared to no EAMC (104 ± 2.1 mmol/l), p<0.0001. There were no differences in %Dehy (EAMC = 2.1 ± 1.1% versus no EAMC = 2.3 ± 0.8%). At the time of EAMC hematocrit = 48 ±1.8%, hemoglobin = 16 ±1.0 mg/dL, lactate = 3.5 ±1.2 mmol/l and serum osmolality = 288 ± 5.6 mOsm/l. CONCLUSIONS: We did not find differences in blood Na+ or K+ when players had EAMC and it did not appear that dehydration or the accumulation of lactate were causative factors. %Dehy (2.1%), Hct (48%) and serum osmolality (288mosm/L) indicated that players with EAMC were only mildly dehydrated (and not different from no EAMC), and lactate (3.5 mmol/l) was not elevated. Low blood Cl-, in many cases clinically low, may play a role in reducing hyperpolarization of the alpha motor neuron thus allowing easier excitation.