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Brendon P. McDermott, Douglas J. Casa, Susan W. Yeargin, Matthew S. Ganio, Rebecca M. Lopez, and Elizabeth A. Mooradian

Context:

Previous field research has not identified sweat rates (SR), fluid consumption (FC), or the efficacy of an educational intervention (EI) for youth during football camp.

Objective:

To measure hydration status and rehydration performance and examine EI using these data.

Design:

Observational with EI randomized comparison.

Participants:

Thirty-three boys (mean ± SD: 12 ± 2 y, 52.9 ± 13.6 kg, 156 ± 12 cm) volunteered during a 5-d camp with 3 (~2-h) sessions per day (WBGT: 25.6 ± 0.5°C).

Main Outcome Measures:

Hydration status, SR, and FC.

Results:

Urine osmolality averaged 796 ± 293 mOsm/L for days 2-5. Game SR (1.30 ± 0.57 L/h) was significantly greater than practice SR (0.65 ± 0.35 L/h; P = .002). Subjects dehydrated during free time but matched fluid losses with FC (0.76 ± 0.29 L/h) during football activities.

Conclusions:

Subjects arrived at camp hypohydrated and maintained this condition. They matched FC and SR during, but dehydrated when not playing, football. This may impair recovery and subsequent performance. Hydration EI seemed to have a positive influence on hydration practices.

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Anita M. Rivera-Brown and José R. Quiñones-González

are great. Sweat rate (SR) typically ranges from 0.5 to 2.0 L/hr ( Sawka et al., 2007 ) and has been reported to be higher than 4 L/hr in American football and tennis and in triathletes ( Baker et al., 2016 ). Regional (7–95.5 mmol/L; Godek et al., 2010 ; Lara et al., 2016 ; Ranchordas et al., 2017

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Yasuki Sekiguchi, Erica M. Filep, Courteney L. Benjamin, Douglas J. Casa, and Lindsay J. DiStefano

that can be used to optimize performance and safety when exercising in the heat. 1 Higher sweat rate, plasma volume expansion, decreased heart rate, and lower internal body temperature are observed following heat acclimation, and these adaptations decrease the risk of heat illness and increase

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Lindsay B. Baker, Michelle A. King, David M. Keyes, Shyretha D. Brown, Megan D. Engel, Melissa S. Seib, Alexander J. Aranyosi, and Roozbeh Ghaffari

factors. Although most basketball practices and games are played in indoor temperate environments, sweating rates can be quite high, ranging up to ∼2.5 L/hr ( Barnes et al., 2019 ; Nuccio et al., 2017 ). High volumes of fluid loss through sweating can increase the risk for significant hypohydration (≥2

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Simone D. Henkin, Paulo L. Sehl, and Flavia Meyer

Because swimmers train in an aquatic environment, they probably do not need to sweat as much as runners who train on land and, therefore, should not develop the same magnitude of sweating adaptations.

Purpose:

To compare sweat rate and electrolyte concentration in swimmers, runners and nonathletes.

Methods:

Ten swimmers (22.9 ± 3.1 years old), 10 runners (25 ± 2.9 y) and 10 nonathletes (26.5 ± 2.2 y) cycled in the heat (32°C and 40% relative humidity) for 30 min at similar intensity relative to their maximal cycle test. Sweat volume was calculated from the difference of their body mass before and after cycling, since they were not allowed to drink. Sweat was collected from the scapula using absorbent patch placed on the skin that was cleaned with distilled water. After cycling, the patch was transferred to syringe and the sample was obtained when squeezing it to a tube. Concentration of sodium ([Na+]), chloride ([Cl–]) and potassium ([K+]) were analyzed using an ion selector analyzer.

Results:

The sweat volume, in liters, of swimmers (0.9 ± 0.3) was lower (P < .05) than that of runners (1.5 ± 0.2) and similar to that of nonathletes (0.6 ± 0.2). [Na+] and [Cl-], in mmolL-1, of swimmers (65.4 ± 5.5 and 61.2 ± 81), and nonathletes (67.3 ± 8.5 and 58.3 ± 9.6) were higher (P < .05) than those of runners (45.2 ± 7.5 and 38.9 ± 8.3). [K+] was similar among groups.

Conclusions:

The lower sweat volume and higher sweat [Na+] and [Cl-] of swimmers, as compared with runners, indicate that training in the water does not cause the same magnitude of sweating adaptations.

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Samuel N. Cheuvront and Robert W. Kenefick

every liter of sweat evaporated from the skin ( Wenger, 1972 ). Large variability in sweating rates (SR), even within sports ( Barnes et al., 2019 ) or within athletes ( Smith et al., 2021 ), lead to generalizations about how much exercise increases daily fluid needs. However, it is the product of SR

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Michael F. Bergeron

A 17-year-old, nationally ranked, male tennis player (AH) had been experiencing heat cramps during tennis match play. His medical history and previous physical exams were unremarkable, and his in-office blood chemistry profiles were normal. On-court evaluation and an analysis of a 3-day dietary record revealed that AH's sweat rate was extensive (2.5 L · hr−1) and that his potential daily on-court sweat sodium losses (89.8 mmol · hr of play') could readily exceed his average daily intake of sodium (87.0-174.0 mmol · day−1). The combined effects of excessive and repeated fluid and sodium losses likely predisposed AH to heat cramps during play. AH was ultimately able to eliminate heat cramps during competition and training by increasing his daily dietary intake of sodium.

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Carl J. Petersen, Marc R. Portus, David B. Pyne, Brian T. Dawson, Matthew N. Cramer, and Aaron D. Kellett

Cricketers are often required to play in hot/humid environments with little time for heat adaptation.

Purpose:

We examined the effect of a short 4-d hot/humid acclimation program on classical physiological indicators of heat acclimation.

Methods:

Male club cricketers were randomly assigned into heat acclimation (ACC, n = 6) or control (CON, n = 6) groups, and 30 min treadmill trials (10 km/h, approx. 30 ± 1.0°C, approx. 65 ± 6% RH) were conducted at baseline and postacclimation. The ACC group completed four high intensity (30–45 min) acclimation sessions on consecutive days at approx. 30°C and approx. 60% RH using a cycle ergometer. The CON group completed matched cycle training in moderate conditions (approx. 20°C, approx. 60% RH). Physiological measures during each treadmill trial included heart rate; core and skin temperatures; sweat Na+, K+ and Cl– electrolyte concentrations; and sweat rate.

Results:

After the 4-d intervention, the ACC group had a moderate decrease of -11 (3 to -24 beats/min; mean and 90% CI) in the 30 min heart rate, and moderate to large reductions in electrolyte concentrations: Na+ -18% (–4 to -31%), K+ -15% (0 to -27%), Cl– -22% (-9 to -33%). Both ACC and CON groups had only trivial changes in core and skin temperatures and sweat rate. After the intervention, both groups perceived they were more comfortable exercising in the heat. The 4-d heat intervention had no detrimental effect on performance.

Conclusions:

Four 30–45 min high intensity cycle sessions in hot/humid conditions elicited partial heat acclimation. For full heat acclimation a more intensive and extensive (and modality-specific) acclimation intervention is needed for cricket players.

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John R. Stofan, Kris L. Osterberg, Craig A. Horswill, Magie Lacambra, E. Randy Eichner, Scott A. Anderson, and Robert Murray

The authors measured 24-h fluid-turnover (FTO) rate during 6 d of preseason training in U.S. college football players. Players, training (T, n = 9, full gear and contact drills) and reference (R, n = 4, conditioning without gear or contact), ingested a deuterium oxide (D2O) dose and provided urine samples every 24 h for analysis of D2O. During one ~2.3–h practice (wet-bulb globe temperature 24.6 °C), body-mass change, urine production, and voluntary fluid intake were measured to calculate gross sweat loss (GSL). Average FTO was 10.3 ± 2.2 L/d for T and 7.0 ± 1.0 L/d for R. GSL was 3.4 ± 1.5 L for T and 1.7 ± 1.3 for R (P > 0.05). By Day 6, body mass decreased significantly in T (–2.4 ± 1.3 kg, P < 0.05) but not in R (0.38 ± 0.95 kg). With preseason training under moderate environmental stress, football players had high FTO and sweat rates, which might have contributed to a loss of body mass during preseason football training.

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Keith C. DeRuisseau, Samuel N. Cheuvront, Emily M. Haymes, and Regina G. Sharp

The purpose of this study was to examine the effects of a 2-hour exercise bout on sweat iron and zinc concentrations and losses in males and females. Nine male and 9 female recreational cyclists exercised at ~50% V̇O2peak in a temperate environment (Ta = 23 °C, RH = 51%). Sweat samples were collected for 15 min during each of four 30-min exercise bouts. No significant differences were observed between males’ and females’ sweat iron or zinc concentrations or losses. Sweat iron concentrations decreased significantly between 60 and 90 min of exercise. Sweating rates increased significantly from 30 to 60 min and remained constant during the second hour. Sweat iron losses were significantly lower during the second hour (0.042 mg/m2/h) than the first hour of exercise (0.060 mg/m2/h). Sweat zinc concentrations also decreased significantly over the 2-hour exercise bout. Dietary intakes of iron and zinc were not significantly correlated to sweat iron and zinc concentrations. Sweat iron and zinc losses during 2 hours of exercise represented 3% and 1% of the RDA for iron and 9% and 8% of the RDA for zinc for men and women, respectively. These results suggest a possible iron conservation that prevents excessive iron loss during prolonged exercise.