Sodium Balance During U. S. Football Training in the Heat: Cramp-Prone vs. Reference Players

Abstract

U. S. football players with a history of heat cramps were evaluated for the effect of physical training, sodium intake, and loss of sweat sodium on whole blood sodium concentration (BNa). Athletes (n=14 males, 24±1 y) were recruited and studied based on medical history, age, and position. The reference group (R, n=8 without a cramping history) and cramp-prone group (C, n=6, history of whole-body cramps associated with extensive sweat loss during exercise in the heat) were measured for body mass and BNa (ISTAT) before and after team training of 2.2 h in hot conditions (WBGT=29–32°C). Intake and loss of fluid and sodium were also measured to determine respective acute balance. In R, BNa was stable pre- to post-training (138.9±1.8 to 139.0±2.0 mmol/L) while it tended to decline in C (137.8±2.3 to 135.7±4.9 mmol/L), and three subjects in C had BNa values below 135 mmol/L (131.7±2.9 mmol/L). C consumed a greater percentage of total fluid as water (p<0.05). Mean sweat sodium concentration was (52.6±29.2 mmol/L for C and 38.3±18.3 mmol/L for R (p>0.05). Compared to R, C tended to experience a decline in BNa and greater acute sodium imbalance. These changes may place cramp-prone players at greater risks for developing acute sodium deficits during training.

Key words

sweat rate - exercise - heat cramps - dehydration - fluid intake - electrolytes

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