Fluid Balance, Sweat Na+ Losses and Carbohydrate Intake in Elite Male Soccer Players Training in Cool Environments

Background/Objectives: Hypohydration increases physiological strain and reduces physical and technical soccer performance. Nonetheless, there are limited data on fluid balance responses in elite soccer players training in cool environments. This study investigated sweat and fluid/carbohydrate intake responses in elite male professional soccer players training at a high intensity in cool environments. Methods: Fluid/sodium (Na+) losses and ad libitum carbohydrate/fluid intake of thirty-six elite male soccer players were measured as part of four training sessions, with each player completing the measurements once. Data were collected under the following conditions classified by ambient temperature (11.3 ± 2.1 °C), wet bulb globe temperature (9.8 ± 3.0 °C), and relative humidity (76.8 ± 10.2%). Mean duration of training sessions was 70 ± 4 min and included soccer-specific training, with players covering a mean total distance of 7054 ± 654 m and 104 ± 9 (m·min−1). Before and after exercise, players were weighed in minimal clothing. During training breaks, players had ad libitum access to carbohydrate beverages and water. Sweat [Na+] (mmol·L−1) was measured by absorbent patches positioned on the upper back. Results: Two out of eleven players displayed a USG score indicative of ‘minimal hypohydration’ (1.022 and 1.022, respectively). Seventeen percent of players experienced hypohydration > 2% of pre-exercise body mass. Mean sweat rate was 1.5 ± 0.4 L·h−1, with individual sweat rates ranging from 0.4–2.2 L·h−1 (outfield players, n = 33). Goalkeepers mean sweat rate was 0.7 ± 0.2 L·h−1 (range 0.6–0.9 L·h−1, n = 3). Sweat [Na+] also varied substantially between players (range 21–49 mmol·L−1), with a mean sweat [Na+] of 35 ± 6.8 mmol·L−1. There was a significant positive correlation between sodium chloride loss and intensity of play (m·min−1) covered during training (rs = 0.368, p = 0.049). Carbohydrate ingestion during training varied between individuals (range 0–25 g·h−1). Conclusions: Sweat rate and sweat sodium chloride loss varies in elite soccer players during high-intensity training in cool environments. Hypohydration exceeded 2% pre-exercise body mass in 17% of players. The ad libitum carbohydrate intake of the players was below recommendations given the intensity and duration of the training sessions.