Sandra Fowkes Godek

Sweat rate and fluid turnover in American football players compared with runners in a hot and humid environment

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.

Hydration status in college football players during consecutive days of twice-a-day preseason practices

Background Football players lose 3.5 to 5 kg of body weight during preseason practices because of heavy sweating. This fluid may be difficult to replace when practices occur 2 times per day on consecutive days. Hypothesis Football players are hypohydrated during twice-a-day preseason training in a hot, humid environment. Study Design Descriptive laboratory study Methods In 10 college football players, body weight was measured, and blood and urine samples were obtained before and after practices on days 2 through 8 of preseason training. Baseline samples were obtained when subjects were euhydrated. Blood samples were used to calculate plasma volume changes. Urine samples were analyzed for specific gravity, sodium, and potassium. Sweat rate was calculated. Core temperature was monitored during half- and full-padded practices. Results Mean wet bulb temperatures were 23.3°C during morning practices and 23.7°C during afternoon practices. Plasma volume was below baseline on day 2 and expanded by day 6. Urine specific gravity was higher than baseline for 12 of 20 measurements over the 8 days. It was 1.0175 ± 0.006 at baseline but subsequently ranged from 1.0214 ± 0.007 to 1.0321 ± 0.004. Mean daily urine sodium dropped from baseline to day 2 (194 ± 43 vs 43 ± 38 mmol × L-1), remaining lower on days 3, 4, and 6 (40 ± 39, 39 ± 39, and 68 ± 40 mmol × L-1, respectively). Urine potassium was lower on days 6 and 8 compared with baseline and day 3. Body weight was below baseline before and after both daily practices. Core temperature was higher in full pads; sweat rate and body weight loss were not different between half and full pads. Conclusion Body weight, plasma volume, urine specific gravity, and urine sodium indicate that football players become dehydrated by day 2 of preseason training. Urine sodium increased to near baseline by day 8; urine specific gravity was elevated. Clinical Relevance Football players struggle to maintain euhydration during preseason twice-a-day sessions.

Sweat Rates, Sweat Sodium Concentrations, and Sodium Losses in 3 Groups of Professional Football Players

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 78.5 degrees F +/- 3.5 degrees F (25.9 degrees C +/- 1.9 degrees C). 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) = 7.3, P = .002). It was lower in BK (1.42 +/- 0.45 L/h) than in LB/QB (1.98 +/- 0.49 L/h) (P < .05) and LM (2.16 +/- 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 = 50 +/- 16 mEq/L, LB/QB = 48.2 +/- 23 mEq/L, and LM = 52.8 +/- 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 = .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.

Sweat Rates and Fluid Turnover in Professional Football Players: A Comparison of National Football League Linemen and Backs

CONTEXT Many National Football League (NFL) teams practice 2 times per day over consecutive days in a hot and humid environment. Large body surface area (BSA) and use of protective equipment result in high sweat rates and total sweat loss in these football players. OBJECTIVE To compare sweat rate, sweat loss, fluid consumption, and weight loss between NFL linemen and backs during preseason practices. DESIGN Between-groups design. SETTING Preseason training camp with wet bulb globe temperature between 19 degrees C and 25 degrees C. PATIENTS OR OTHER PARTICIPANTS Eight linemen and 4 backs and receivers participated. MAIN OUTCOME MEASURE(S) Data were collected during both practice sessions on 2 separate days during the first week of August. Sweat rate was calculated as change in mass adjusted for all fluids consumed between prepractice and postpractice body mass measurements and the urine produced during practice divided by the length of the practice session. Gross daily sweat losses also were calculated. RESULTS Height, mass, and BSA were higher in linemen than in backs. Sweat rate was also higher in linemen (2385 +/- 520 mL/h) than in backs (1410 +/- 660 mL/h, P < .001), as was the total volume of sweat lost during both practices in 1 day (6870 +/- 1034 mL/d versus 4110 +/- 2287 mL/d, P = .014). Compared with backs, linemen consumed more fluids during practice (2030 +/- 849 mL versus 1179 +/- 753 mL, P = .025) but produced less urine (53 +/- 73 mL versus 163 +/- 141 mL, P = .018). There was no difference in postpractice weight loss (linemen = -1.15 +/- 0.83%, backs = -1.06 +/- 0.76%). CONCLUSIONS 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.

Fluid Consumption and Sweating in National Football League and Collegiate Football Players With Different Access to Fluids During Practice

CONTEXT Considerable controversy regarding fluid replacement during exercise currently exists. OBJECTIVE To compare fluid turnover between National Football League (NFL) players who have constant fluid access and collegiate football players who replace fluids during water breaks in practices. DESIGN Observational study. SETTING Respective preseason training camps of 1 National Collegiate Athletic Association Division II (DII) football team and 1 NFL football team. Both morning and afternoon practices for DII players were 2.25 hours in length, and NFL players practiced for 2.25 hours in the morning and 1 hour in the afternoon. Environmental conditions did not differ. PATIENTS OR OTHER PARTICIPANTS Eight NFL players (4 linemen, 4 backs) and 8 physically matched DII players (4 linemen, 4 backs) participated. INTERVENTION(S) All players drank fluids only from their predetermined individual containers. The NFL players could consume both water and sports drinks, and the DII players could only consume water. MAIN OUTCOME MEASURE(S) We measured fluid consumption, sweat rate, total sweat loss, and percentage of sweat loss replaced. Sweat rate was calculated as change in mass adjusted for fluids consumed and urine produced. RESULTS Mean sweat rate was not different between NFL (2.1 +/- 0.25 L/h) and DII (1.8 +/- 0.15 L/h) players (F(1,12) = 2, P = .18) but was different between linemen (2.3 +/- 0.2 L/h) and backs (1.6 +/- 0.2 L/h) (t(14) = 3.14, P = .007). We found no differences between NFL and DII players in terms of percentage of weight loss (t(7) = -0.03, P = .98) or rate of fluid consumption (t(7) = -0.76, P = .47). Daily sweat loss was greater in DII (8.0 +/- 2.0 L) than in NFL (6.4 +/- 2.1 L) players (t(7) = -3, P = .02), and fluid consumed was also greater in DII (5.0 +/- 1.5 L) than in NFL (4.0 +/- 1.1 L) players (t(7) = -2.8, P = .026). We found a correlation between sweat loss and fluids consumed (r = 0.79, P < .001). CONCLUSIONS 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.

Changes in Blood Electrolytes and Plasma Volume in National Football League Players During Preseason Training Camp

Blood samples were drawn from 6 National Football League players for baseline measures and then prior to morning practice on days 3, 5, and 9. Mean blood sodium level was lower on days 3 (136.9±0.6 mmol·L -1 ) and day 5 (138.1±0.6 mmol·L -1 ) compared to baseline (140.4±0.4 mmol·L -1 ) and day 9 (140.3±0.4 mmol·L -1 ). Mean blood potassium level was higher on day 5 (4.16±0.13 mmol·L -1 ) and day 9 (4.36±0.08 mmol·L -1 ) compared to baseline (3.77±0.15 mmol·L -1 ). Mean plasma volume was lower on day 3 (-4.9%±2.4%) compared to day 5 (4.5%±1.9%), and mean mass (days 2 through 9) was below baseline before and after practices. Blood sodium level declined by day 3 of preseason and was maintained at low normal levels at the expense of contracted plasma volume. Increased resting blood potassium levels on days 5 and 9 indicated rhabdomyolysis. Increased consumption of sodium is important for professional football players to maintain plasma volume during the first week of preseason.

Cold-Water Immersion Cooling Rates in Football Linemen and Cross-Country Runners With Exercise-Induced Hyperthermia

CONTEXT   Ideal and acceptable cooling rates in hyperthermic athletes have been established in average-sized participants. Football linemen (FBs) have a small body surface area (BSA)-to-mass ratio compared with smaller athletes, which hinders heat dissipation. OBJECTIVE   To determine cooling rates using cold-water immersion in hyperthermic FBs and cross-country runners (CCs). DESIGN   Cohort study. SETTING   Controlled university laboratory. PATIENTS OR OTHER PARTICIPANTS   Nine FBs (age = 21.7 ± 1.7 years, height = 188.7 ± 4 cm, mass = 128.1 ± 18 kg, body fat = 28.9% ± 7.1%, lean body mass [LBM] = 86.9 ± 19 kg, BSA = 2.54 ± 0.13 m2, BSA/mass = 201 ± 21.3 cm2/kg, and BSA/LBM = 276.4 ± 19.7 cm2/kg) and 7 CCs (age = 20 ± 1.8 years, height = 176 ± 4.1 cm, mass = 68.7 ± 6.5 kg, body fat = 10.2% ± 1.6%, LBM = 61.7 ± 5.3 kg, BSA = 1.84 ± 0.1 m2, BSA/mass = 268.3 ± 11.7 cm2/kg, and BSA/LBM = 298.4 ± 11.7 cm2/kg). INTERVENTION(S)   Participants ingested an intestinal sensor, exercised in a climatic chamber (39°C, 40% relative humidity) until either target core temperature (Tgi) was 39.5°C or volitional exhaustion was reached, and were immediately immersed in a 10°C circulated bath until Tgi declined to 37.5°C. A general linear model repeated-measures analysis of variance and independent t tests were calculated, with P < .05. MAIN OUTCOME MEASURE(S)   Physical characteristics, maximal Tgi, time to reach 37.5°C, and cooling rate. RESULTS   Physical characteristics were different between groups. No differences existed in environmental measures or maximal Tgi (FBs = 39.12°C ± 0.39°C, CCs = 39.38°C ± 0.19°C; P = .12). Cooling times required to reach 37.5°C (FBs = 11.4 ± 4 minutes, CCs = 7.7 ± 0.06 minutes; P < .002) and therefore cooling rates (FBs = 0.156°C·min-1 ± 0.06°C·min-1, CCs = .255°C·min-1 ± 0.05°C·min-1; P < .002) were different. Strong correlations were found between cooling rate and body mass (r = -0.76, P < .001), total BSA (r = -0.74, P < .001), BSA/mass (r = 0.73, P < .001), LBM/mass (r = 0.72, P < .002), and LBM (r = -0.72, P < .002). CONCLUSIONS   With cold-water immersion, the cooling rate in CCs (0.255°C·min-1) was greater than in FBs (0.156°C·min-1); however, both were considered ideal (≥0.155°C·min-1). Athletic trainers should realize that it likely takes considerably longer to cool large hyperthermic American-football players (>11 minutes) than smaller, leaner athletes (7.7 minutes). Cooling rates varied widely from 0.332°C·min-1 in a small runner to only 0.101°C·min-1 in a lineman, supporting the use of rectal temperature for monitoring during cooling.