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

U.S. football players with a history of heatcramps 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 2.2h in hot conditions (WBGT=29-32 degrees 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 +/- 23 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 mmoI/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.