Football players struggle to maintain euhydration during preseason twice-a-day sessions.

Objectives: To determine sweat rate (SwR) and fluid requirements for American footballers practicing in a hot, humid environment compared with cross country runners in the same conditions. Methods: Fifteen subjects, 10 footballers and five runners, participated. On the 4th and 8th day of preseason two a day practices, SwR during exercise was determined in both morning and afternoon practices/runs from the change in body mass adjusted for fluids consumed and urine produced. Unpaired t tests were used to determine differences between groups. Results: Overall SwR measured in litres/h was higher in the footballers than the cross country runners (2.14 (0.53) v 1.77 (0.4); p,0.01). Total sweat loss in both morning (4.83 (1.2) v 1.56 (0.39) litres) and afternoon (4.8 (1.2) v 1.97 (0.28) litres) practices/runs, and daily sweat losses (9.4 (2.2) v 3.53 (0.54) litres) were higher in the footballers (p,0.0001). The footballers consumed larger volumes of fluid during both morning and afternoon practices/runs (23.9 (8.9) v 5.5 (3.1) ml/min and 23.5 (7.3) v 13.6 (5.6) ml/min; p,0.01). For complete hydration, the necessary daily fluid consumption calculated as 130% of daily sweat loss in the footballers was 12.2 (2.9) litres compared with 4.6 (0.7) litres in the runners (p,0.0001). Calculated 24 hour fluid requirements in the footballers ranged from 8.8 to 19 litres. Conclusions: The American footballers had a high SwR with large total daily sweat losses. Consuming large volumes of hypotonic fluid may promote sodium dilution. Recommendations for fluid and electrolyte replacement must be carefully considered and monitored in footballers to promote safe hydration and avoid hyponatraemia.

Linemen sweated at higher rates, lost larger volumes of sweat, consumed more fluids, and produced less urine during practice compared with the physically smaller backs, but they did not lose a greater percentage of body weight. Sodium losses could be considerable in NFL players during the preseason because of high daily sweat losses in backs and in linemen.

Context: Sweat sodium losses have never been reported in a large cohort of American football players.Objective: To compare sweat rates (SwtRs), sweat sodium concentrations (SwtNa + ), and sodium losses in 3 groups of players (backs and receivers [BK], linebackers and quarterbacks [LB/QB], and linemen [LM]) to determine if positional differences and, therefore, size differences exist.Design: Observational study. Setting: Data were collected during practices in the second week of 2 consecutive training camps. The wet bulb globe temperature was 78.56F 6 3.56F (25.96C 6 1.96C).Patients or Other Participants: Eighteen BK, 12 LB/QB, and 14 LM volunteered.Intervention(s): Sterile sweat patches were applied to the right forearm after the skin was appropriately cleaned. The patches were removed during practice, placed in sterile tubes, centrifuged, frozen, and later analyzed by flame photometry.Main Outcome Measure(s): Sweat rate, SwtNa + , and sodium loss. We calculated SwtR by change in mass adjusted for urine produced and fluids consumed divided by practice time in hours.Results: Other than age, physical characteristics were different among groups (P , .001). The SwtR was different among groups (F 2,41 5 7.3, P 5 .002). It was lower in BK (1.42 6 0.45 L/h) than in LB/QB (1.98 6 0.49 L/h) (P , .05) and LM (2.16 6 0.75 L/h) (P , .01), but we found no differences between SwtRs for LB/QB and LM. The SwtNa + was not different among groups (BK 5 50 6 16 mEq/L, LB/QB 5 48.2 6 23 mEq/L, and LM 5 52.8 6 25 mEq/L) and ranged from 15 to 99 mEq/L. Sweat sodium losses ranged from 642 mg/h to 6.7 g/ h, and findings for group comparisons approached significance (P 5 .06). On days when players practiced 4.5 hours, calculated sodium losses ranged from 2.3 to 30 g/d.Conclusions: The BK sweated at lower rates than did the midsized LB/QB and large LM, but LB/QB sweated similarly to LM. Sweat sodium concentration and daily sodium losses ranged considerably. Heavy, salty sweaters require increased dietary consumption of sodium during preseason.

During preseason practices, the DII players drinking water at water breaks replaced the same volume of fluid (66% of weight lost) as NFL players with constant access to both water and sports drinks.