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Ronald J. Maughan, Lisa A. Dargavel, Rachael Hares and Susan M. Shirreffs

This study investigated fluid and electrolyte balance in well-trained male and female swimmers during 2 training sessions. Participants were 17 nationally ranked swimmers measured during a period of intensive training. Sweat loss was assessed from changes in body mass after correction for fluid intake and urine collection. Sweat composition was measured from waterproof absorbent patches applied at 4 skin sites. Air and pool-water temperatures were 36 °C and 27.4 °C, respectively. Training lasted 105 min in each session. All measured variables were similar on the 2 testing days. Mean sweat-volume loss was 548 ± 243 ml, and mean sweat rate was 0.31 ± 0.1 L/hr. Mean fluid intake was 489 ± 270 ml. Mean body-mass loss was 0.10 ± 0.50 kg, equivalent to 0.1% ± 0.7% dehydration. Mean pretraining urine osmolality was 662 ± 222 mOsm/kg, which was negatively associated with both mean drink volume consumed (p = .044, r 2 = .244) and mean urine volume produced during training (p = .002, r 2 = .468). Mean sweat Na+, K+, and Cl concentrations (mmol/L) were 43 ± 14, 4 ± 1, and 31± 9, respectively; values were not different between males and females and were not different between days except for a marginal difference in K+ concentration. The average swimmer remained hydrated during the session, and calculated sweat rates were similar to those in previous aquatic studies.

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Matthew T. Wittbrodt, Mindy Millard-Stafford, Ross A. Sherman and Christopher C. Cheatham

Purpose:

The impact of mild hypohydration on physiological responses and cognitive performance following exercise-heat stress (EHS) were examined compared with conditions when fluids were ingested ad libitum (AL) or replaced to match sweat losses (FR).

Methods:

Twelve unacclimatized, recreationally-active men (22.2 ± 2.4 y) completed 50 min cycling (60%VO2peak) in the heat (32°C; 65% RH) under three conditions: no fluid (NF), AL, and FR. Before and after EHS, a cognitive battery was completed: Trail making, perceptual vigilance, pattern comparison, match-to-sample, and letter-digit recognition tests.

Results:

Hypohydration during NF was greater compared with AL and FR (NF: -1.5 ± 0.6; AL: -0.3 ± 0.8; FR: -0.1 ± 0.3% body mass loss) resulting in higher core temperature (by 0.4, 0.5 °C), heart rate (by 13 and 15 b·min-1), and physiological strain (by 1.3, 1.5) at the end of EHS compared with AL and FR, respectively. Cognitive performance (response time and accuracy) was not altered by fluid condition; however, mean response time improved (p < .05) for letter-digit recognition (by 56.7 ± 85.8 ms or 3.8%; p < .05) and pattern comparison (by 80.6 ± 57.4 ms or 7.1%; p < .001), but mean accuracy decreased in trail making (by 1.2 ± 1.4%; p = .01) after EHS (across all conditions).

Conclusions:

For recreational athletes, fluid intake effectively mitigated physiological strain induced by mild hypohydration; however, mild hypohydration resulting from EHS elicited no adverse changes in cognitive performance.

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David J. Clayton, Gethin H. Evans and Lewis J. James

The purpose of this study was to examine the gastric emptying and rehydration effects of hypotonic and hypertonic glucose-electrolyte drinks after exercise-induced dehydration. Eight healthy males lost ~1.8% body mass by intermittent cycling and rehydrated (150% of body mass loss) with a hypotonic 2% (2% trial) or a hypertonic 10% (10% trial) glucose-electrolyte drink over 60 min. Blood and urine samples were taken at preexercise, postexercise, and 60, 120, 180, and 240 min postexercise. Gastric and test drink volume were determined 15, 30, 45, 60, 90, and 120 min postexercise. At the end of the gastric sampling period 0.3% (2% trial) and 42.1% (10% trial; p < .001) of the drinks remained in the stomach. Plasma volume was lower (p < .01) and serum osmolality was greater (p < .001) at 60 and 120 min during the 10% trial. At 240 min, 52% (2% trial) and 64% (10% trial; p < .001) of the drinks were retained. Net fluid balance was greater from 120 min during the 10% trial (p < .001). When net fluid balance was corrected for the volume of fluid in the stomach, it was greater at 60 and 120 min during the 2% trial (p < .001). These results suggest that the reduced urine output following ingestion of a hypertonic rehydration drink might be mediated by a slower rate of gastric emptying, but the slow gastric emptying of such solutions makes rehydration efficiency difficult to determine in the hours immediately after drinking, compromising the calculation of net fluid balance.

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Ben Desbrow, Daniel Murray and Michael Leveritt

Purpose:

To investigate the effect of manipulating the alcohol and sodium content of beer on fluid restoration following exercise.

Method:

Seven male volunteers exercised on a cycle ergometer until 1.96 ± 0.25% body mass (mean± SD) was lost. Participants were then randomly allocated a different beer to consume on four separate occasions. Drinks included a low-alcohol beer (2.3% ABV; LightBeer), a low-alcohol beer with 25 mmol×L−1 of added sodium (LightBeer+25), a full-strength beer (4.8% ABV; Beer), or a full-strength beer with 25 mmol×L−1 of added sodium (Beer+25). Volumes consumed were equivalent to 150% of body mass loss during exercise and were consumed over a 1h period. Body mass and urine samples were obtained before and hourly for 4 hr after beverage consumption.

Results:

Significantly enhanced net fluid balance was achieved following the LightBeer+25 trial (–1.02 ± 0.35 kg) compared with the Beer (–1.59 ± 0.32 kg) and Beer+25 (–1.64 ± 0.28 kg) treatments. Accumulated urine output was significantly lower in the LightBeer+25 trial (1477 ± 485 ml) compared with the Beer+25 (2101 ± 482 ml) and Beer (2175 ± 372 ml) trials.

Conclusion:

A low alcohol beer with added sodium offers a potential compromise between a beverage with high social acceptance and one which avoids the exacerbated fluid losses observed when consuming full strength beer.

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Gethin H. Evans, Jennifer Miller, Sophie Whiteley and Lewis J. James

The purpose of this study was to examine the efficacy of water and a 50 mmol/L NaCl solution on postexercise rehydration when a standard meal was consumed during rehydration. Eight healthy participants took part in two experimental trials during which they lost 1.5 ± 0.4% of initial body mass via intermittent exercise in the heat. Participants then rehydrated over a 60-min period with water or a 50 mmol/L NaCl solution in a volume equivalent to 150% of their body mass loss during exercise. In addition, a standard meal was ingested during this time which was equivalent to 30% of participants predicted daily energy expenditure. Urine samples were collected before and after exercise and for 3 hr after rehydration. Cumulative urine volume (981 ± 458 ml and 577 ± 345 mL; p = .035) was greater, while percentage fluid retained (50 ± 20% and 70 ± 21%; p = .017) was lower during the water compared with the NaCl trial respectively. A high degree of variability in results was observed with one participant producing 28% more urine and others ranging from 18–83% reduction in urine output during the NaCl trial. The results of this study suggest that after exercise induced dehydration, the ingestion of a 50 mmol/L NaCl solution leads to greater fluid retention compared with water, even when a meal is consumed postexercise. Furthermore, ingestion of plain water may be effective for maintenance of fluid balance when food is consumed in the rehydration period.

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Ronald J. Maughan, Stuart J. Merson, Nick P. Broad and Susan M. Shirreffs

This study measured fluid balance during a 90-min preseason training session in the first team squad (24 players) of an English Premier League football team. Sweat loss was assessed from changes in body mass after correction for ingested fluids and urine passed. Sweat composition was measured by collection from patches attached to the skin at 4 sites. The weather was warm (24-29 °C), with moderate humidity (46–64%). The mean ± SD body mass loss over the training session was 1.10 ± 0.43 kg, equivalent to a level of dehydration of 1.37 ± 0.54% of the pre-training body mass. Mean fluid intake was 971 ± 303 ml. Estimated total mean sweat loss was 2033 ±413 ml. Mean sweat electrolyte concentrations (mmol/L) were: sodium,49± 12; potassium,6.0± 1.3;chloride, 43 ± 10. Total sweat sodium loss of 99 ± 24 mmol corresponds to a salt (sodium chloride) loss of 5.8 ± 1.4 g. Mean urine osmolality measured on pre-training samples provided by the players was 666 ±311 mosmol/kg (n=21). These data indicate that sweat losses of water and solute in football players in training can be substantial but vary greatly between players even with the same exercise and environmental conditions. Voluntary fluid intake also shows wide inter-individual variability and is generally insufficient to match fluid losses.

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Susan M. Shirreffs, Luis F. Aragon-Vargas, Mhairi Keil, Thomas D. Love and Sian Phillips

To determine the effectiveness of 3 commonly used beverages in restoring fluid and electrolyte balance, 8 volunteers dehydrated by 1.94% ± 0.17% of body mass by intermittent exercise in the heat, then ingested a carbohydrate-electrolyte solution (Gatorade), carbonated water/apple-juice mixture (Apfelschorle), and San Benedetto mineral water in a volume equal to 150% body-mass loss. These drinks are all are perceived to be effective rehydration solutions, and their effectiveness was compared with the rehydration effectiveness of Evian mineral water, which is not perceived in this way by athletes. Four hours after rehydration, the subjects were in a significantly lower hydration status than the pretrial situation on trials with Apfelschorle (–365 ± 319 mL, P = 0.030), Evian (–529 ± 319 mL, P < 0.0005), and San Benedetto (–401 ± 353 mL, P = 0.016) but were in the same hydration status as before the dehydrating exercise on Gatorade (–201 ± 388 mL, P = 0.549). Sodium balance was negative on all trials throughout the study; only with Apfelschorle did subjects remain in positive potassium balance. In this scenario, recovery of fluid balance can only be achieved when significant, albeit insufficient, quantities of sodium are ingested after exercise. There is a limited range of commercially available products that have a composition sufficient to achieve this, even though the public thinks that some of the traditional drinks are effective for this purpose.

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Lewis J. James and Susan M. Shirreffs

Weight categorized athletes use a variety of techniques to induce rapid weight loss (RWL) in the days leading up to weigh in. This study examined the fluid and electrolyte balance responses to 24-hr fluid restriction (FR), energy restriction (ER) and fluid and energy restriction (F+ER) compared with a control trial (C), which are commonly used techniques to induce RWL in weight category sports. Twelve subjects (six male, six female) received adequate energy and water (C) intake, adequate energy and restricted water (~10% of C; FR) intake, restricted energy (~25% of C) and adequate water (ER) intake or restricted energy (~25% of C) and restricted (~10% of C) water intake (F+ER) in a randomized counterbalanced order. Subjects visited the laboratory at 0 hr, 12 hr, and 24 hr for blood and urine sample collection. Total body mass loss was 0.33% (C), 1.88% (FR), 1.97% (ER), and 2.44% (F+ER). Plasma volume was reduced at 24 hr during FR, ER, and F+ER, while serum osmolality was increased at 24 hr for FR and F+ER and was greater at 24 hr for FR compared with all other trials. Negative balances of sodium, potassium, and chloride developed during ER and F+ER but not during C and FR. These results demonstrate that 24 hr fluid and/or energy restriction significantly reduces body mass and plasma volume, but has a disparate effect on serum osmolality, resulting in hypertonic hypohydration during FR and isotonic hypohydration during ER. These findings might be explained by the difference in electrolyte balance between the trials.

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Nicholas Gant, Ajmol Ali and Andrew Foskett

Carbohydrate and caffeine are known to independently improve certain aspects of athletic performance. However, less is understood about physiological and performance outcomes when these compounds are coingested in a rehydration and carbohydrate-replacement strategy. The aim of this study was to examine the influence of adding a moderate dose of caffeine to a carbohydrate solution during prolonged soccer activity. Fifteen male soccer players performed two 90-min intermittent shuttle-running trials. They ingested a carbohydrate-electrolyte solution (CON) providing a total of 1.8 g/kg body mass (BM) of carbohydrate or a similar solution with added caffeine (CAF; 3.7 mg/kg BM). Solutions were ingested 1 hr before exercise and every 15 min during the protocol. Soccer passing skill and countermovement-jump height (CMJ) were quantified before exercise and regularly during exercise. Sprinting performance, heart rate, blood lactate concentration (La) and the subjective experiences of participants were measured routinely. Mean 15-m sprint time was faster during CAF (p = .04); over the final 15 min of exercise mean sprint times were CAF 2.48 ± 0.15 s vs. CON 2.59 ± 0.2 s. Explosive leg power (CMJ) was improved during CAF (52.9 ± 5.8 vs. CON 51.7 ± 5.7 cm, p = .03). Heart rate was elevated throughout CAF, and ratings of pleasure were significantly enhanced. There were no significant differences in passing skill, rating of perceived exertion, La, or body-mass losses between trials. The addition of caffeine to the carbohydrate-electrolyte solution improved sprinting performance, countermovement jumping, and the subjective experiences of players. Caffeine appeared to offset the fatigue-induced decline in self-selected components of performance.

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James P. Morton, Colin Robertson, Laura Sutton and Don P. M

Professional boxing is a combat sport categorized into a series of weight classes. Given the sport’s underpinning culture, boxers’ typical approach to “making weight” is usually via severe acute and/or chronic energy restriction and dehydration. Such practices have implications for physical performance and also carry health risks. This article provides a case-study account outlining a more structured and gradual approach to helping a professional male boxer make weight for the 59-kg superfeatherweight division. Over a 12-week period, the client athlete adhered to a daily diet approximately equivalent to his resting metabolic rate (6–7 MJ; 40% carbohydrate, 38% protein, 22% fat). Average body-mass loss was 0.9 ± 0.4 kg/wk, equating to a total loss of 9.4 kg. This weight loss resulted in a decrease in percent body fat from 12.1% to 7.0%. In the 30 hr between weigh-in and competition, the client consumed a high-carbohydrate diet (12 g/kg body mass) supported by appropriate hydration strategies and subsequently entered the ring at a fighting weight of 63.2 kg. This nutritional strategy represented a major change in the client’s habitual weight-making practices and did not rely on any form of intended dehydration during the training period or before weighing in. The intervention demonstrates that a more gradual approach to making weight in professional boxing can be successfully achieved via a combination of restricted energy intake and increased energy expenditure, providing there is willingness on the part of the athlete and coaches involved to adopt novel practices.