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Alexander S.D. Gamble, Jessica L. Bigg, Tyler F. Vermeulen, Stephanie M. Boville, Greg S. Eskedjian, Sebastian Jannas-Vela, Jamie Whitfield, Matthew S. Palmer and Lawrence L. Spriet

Fluid Intake, Sweat Loss, and Body Mass Loss of JR, AHL, and NHL Players During On-Ice Practices JR ( n  = 77) AHL ( n  = 60) NHL ( n  = 77) Urine specific gravity  All players 1.018 ± 0.007 1.019 ± 0.007 1.018 ± 0.008  Goalies 1.021 ± 0.006 1.019 ± 0.002 1.025 ± 0.006  Defensemen 1.015 ± 0.007 1

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Eric K. O’Neal, Brett A. Davis, Lauren K. Thigpen, Christina R. Caufield, Anthony D. Horton and Joyce R. McIntosh

The purpose of this study was to determine how accurately runners estimate their sweat losses. Male (n = 19) and female (n = 20) runners (41 ± 10 yr, VO2max 57 ± 9 ml · kg−1 · min−1) from the southeastern U.S. completed an ~1-hr run during late summer on a challenging outdoor road course (wet bulb globe temperature 24.1 ± 1.5 °C). Runs began at ~6:45 a.m. or p.m. Before and after running, participants filled race-aid-station paper cups with a volume of fluid they felt would be equivalent to their sweat losses. Total sweat losses and losses by percent body weight differed (p < .01) between men (1,797 ± 449 ml, 2.3% ± 0.6%) and women (1,155 ± 258 ml, 1.9% ± 0.4%). Postrun estimates (738 ± 470 ml) were lower (p < .001) than sweat losses (1,468 ± 484 ml), equaling underestimations of 50% ± 23%, with no differences in estimation accuracy by percentage between genders. Runners who reported measuring changes in pre- and postrun weight to assess sweat losses within the previous month (n = 9, –54% ± 18%) were no more accurate (p = .55) than runners who had not (n = 30, –48% ± 24%). These results suggest that inadequate fluid intake during runs or between runs may stem from underestimations of sweat losses and that runners who do assess sweat-loss changes may be making sweat-loss calculation errors or do not accurately translate changes in body weight to physical volumes of water.

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Dennis Passe, Mary Horn, John Stofan, Craig Horswill and Robert Murray

This study investigated the relationship between runners’ perceptions of fluid needs and drinking behavior under conditions of compensable heat stress (ambient temperature = 20.5 ± 0.7 °C, 68.9 °F; relative humidity = 76.6%). Eighteen experienced runners (15 men, 40.5 ± 2.5 y, and 3 women, 42 ± 2.3 y) were given ad libitum access to a sports drink (6% carbohydrate-electrolyte solution) at Miles 2, 4, 6, and 8. After the run (75.5 ± 8.0 min), subjects completed questionnaires that required them to estimate their individual fluid intake and sweat loss. Dehydration averaged 1.9% ± 0.8% of initial body weight (a mean sweat loss of 21.6 ± 5.1 mL·kg−1·h−1). Subjects replaced only 30.5% ± 18.1% of sweat loss and underestimated their sweat loss by 42.5% ± 36.6% (P ≤ 0.001). Subjects’ self-estimations of fluid intake (5.2 ± 3.2 mL·kg−1·h−1) were not significantly different from actual fluid intake (6.1 ± 3.4 mL·kg−1·h−1) and were significantly correlated (r = 0.63, P = 0.005). The data indicate that even under favorable conditions, experienced runners voluntarily dehydrate (P ≤ 0.001), possibly because they are unable to accurately estimate sweat loss and consequently cannot subjectively judge how much fluid to ingest to prevent dehydration. This conclusion suggests that runners should not depend on self-assessment to maintain adequate hydration, underscores the need for runners to enhance their ability to self-assess sweat losses, and suggests that a predetermined regimen of fluid ingestion might be necessary if they wish to maintain more optimal hydration.

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Ronald J. Maughan, Phillip Watson, Gethin H. Evans, Nicholas Broad and Susan M. Shirreffs

Fluid balance and sweat electrolyte losses were measured in the players and substitutes engaged in an English Premier League Reserve competitive football match played at an ambient temperature of 6–8 °C (relative humidity 50–60%). Intake of water and/or sports drink and urine output were recorded, and sweat composition was estimated from absorbent swabs applied to 4 skin sites for the duration of the game. Body mass was recorded before and after the game. Data were obtained for 22 players (age 21 y, height 180 cm, mass 78 kg) and 9 substitutes (17 y, 181 cm, 72 kg). All were male. Two of the players were dismissed during the game, and none of the substitutes played any part in the game. Mean ± SD sweat loss of players amounted to 1.68 ± 0.40 L, and mean fluid intake was 0.84 ± 0.47 L (n = 20), with no difference between teams. Corresponding values for substitutes, none of whom played in the match, were 0.40 ± 0.24 L and 0.78 ± 0.46 L (n = 9). Prematch urine osmolality was 678 ± 344 mOsm/kg: 11 of the 31 players provided samples with an osmolality of more than 900 mOsm/kg. Sweat sodium concentration was 62 ± 13 mmol/L, and total sweat sodium loss during the game was 2.4 ± 0.8 g. These descriptive data show a large individual variability in hydration status, sweat losses, and drinking behaviors in a competitive football match played in a cool environment, highlighting the need for individualized assessment of hydration status to optimize fluid-replacement strategies.

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Jason R. Boynton, Fabian Danner, Paolo Menaspà, Jeremiah J. Peiffer and Chris R. Abbiss

2 max and used to calculate T  > 90% VO 2 max. Sweat loss was calculated by subtracting the nude bodyweight after exercise from the nude bodyweight prior to exercise and amount of water consumed during exercise. Water consumed during exercise was determined by measuring pre and post water bottle

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Eric Kyle O’Neal, Samantha Louise Johnson, Brett Alan Davis, Veronika Pribyslavska and Mary Caitlin Stevenson-Wilcoxson

 al., 2000 ; Convertino et al., 1996 ; McDermott et al., 2017 ; Sawka et al., 2007 ) and opposing viewpoints concerning these guidelines ( Beltrami et al., 2008 ; Hew-Butler et al., 2005 ). Sweat loss volume must first be established if prescribed fluid intake is to be incorporated before, during, or

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Elizabeth M. Broad, Louise M. Burke, Greg R. Cox, Prue Heeley and Malcolm Riley

Fluid losses (measured by body weight changes) and voluntary fluid intakes were measured in elite basketball, netball, and soccer teams during typical summer and winter exercise sessions to determine fluid requirements and the degree of fluid replacement. Each subject was weighed in minimal clothing before and immediately after training, weights, and competition sessions; fluid intake, duration of exercise, temperature and humidity, and opportunity to drink were recorded. Sweat rates were greatest during competition sessions and significantly lower during weights sessions for all sports. Seasonal variation in dehydration (%DH) was not as great as may have been expected, particularly in sports played indoors. Factors influencing fluid replacement during exercise included provision of an individual water bottle, proximity to water bottles during sessions, encouragement to drink, rules of the game, duration and number of breaks or substitutions, and awareness of personal sweat rates. Guidelines for optimizing fluid intakes in these three sports are provided.

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Karianne Backx, Ken A. van Someren and Garry S. Palmer

This study investigated the effect of differing fluid volumes consumed during exercise, on cycle time-trial (TT) performance conducted under thermoneutral conditions (20 °C, 70% RH). Ten minutes after consuming a bolus of 6 ml · kg−1 body mass (BM) of a 6.4% CHO solution and immediately following a warm-up, 8 male cyclists undertook a 1-h self-paced TT on 4 separate occasions. During a “familiarization” trial, subjects were given three 5-min periods (15– 20 min, 30–35 min, and 45–50 min) to consume fluid ad libitum. Thereafter subjects undertook, in random order, trials consuming high (HF), moderate (MF), or low fluid (LF) volumes, where 300, 150, and 40 ml of fluid were consumed at 15, 30, and 45 min of each trial, respectively, and total CHO intake was maintained at 57.6 g. During exercise, power output and heart rate were monitored continuously, whilst stomach fullness was rated every 10 min. Additionally, BM loss and BM loss corrected for fluid intake was calculated during each trial. At 40, 50, and 60 min differences in ratings of stomach fullness were found between trials (LF vs. HF and MF vs. HF). There were however no differences in performance or physiological variables (heart rate or BM loss) between trials. These results indicate that when a pre-exercise CHO bolus is consumed, there is no effect of subsequent consumption of different fluid volumes when trained cyclists undertake a 1-h performance task in a thermoneutral environment.

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Michelle R. Minehan, Malcolm D. Riley and Louise M. Burke

A palatable flavor is known to enhance fluid intake during exercise; however, a fear of excessive kilojoule intake may deter female athletes from consuming a sports drink during training sessions. In order to examine this issue, we monitored fluid balance during 9 separate training sessions undertaken by junior elite female netball players (n = 9), female basketball players (n = 7), and male basketball players (n = 8). The beverages tested were water, a regular carbohydrate-electrolyte beverage (6.8% CHO, 18.7 mmol/L Na, 3.0 mmol/L K, 1130 kJ/L), and an identical tasting, low kilojoule electrolyte beverage (1% CHO, 18.7 mmol/L Na, 3.0 mmol/L K, 170 kJ/L). Each subject received each of the 3 drinks at 3 separate training sessions, in a randomized, balanced order. Subjects were aware of the beverage provided. Change in body mass over the training session was used to estimate body fluid change, while voluntary fluid intake was determined from the change in weight of drink bottles used in each session. The overall fluid balance on drinks classified as regular, low kilojoule, and water was -11.3 ml/h (95%CI -99.6 to 77.0), -29.5 ml/h (95%CI -101.4 to 42.5) and -156.4 ml/h (95%CI -215.1 to -97.6), respectively. The results indicate that, overall, better fluid balance was achieved using either of the flavored drinks compared to water. These data confirm that flavored drinks enhance fluid balance in a field situation, and suggest that the energy content of the drink is relatively unimportant in determining voluntary fluid intake.

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Douglas J. Casa, Samuel N. Cheuvront, Stuart D. Galloway and Susan M. Shirreffs

, 2004 ; IOC Consensus Statement, 2011 ). Dehydration impairs performance in most events, and athletes should be well hydrated before exercise. Sufficient fluid should be consumed during exercise to limit dehydration to less than about 2% of body mass. . . . Sodium should be included when sweat losses