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Cristina Palacios, Karin Wigertz and Connie M. Weaver

Purpose:

To compare dermal electrolyte loss between whole body and regional patch methods in women during 24-h.

Methods:

Dermal loss was collected in 6 healthy women mean age 27 ± 4 years, while consuming 936 mg/d sodium, 1764 mg/d potassium, 696 mg/d calcium, and 152 mg/d magnesium. Twenty-four hour whole body dermal loss was collected using cotton suits by a washdown procedure. Twenty-four hour patch loss was collected from 8 patches placed on the legs, arms, and back.

Results:

Dermal loss from whole body was 108 ± 110 mg/d sodium, 133 ± 87 mg/d potassium, 103 ± 22 mg/d calcium, and 35 ± 13 mg/d magnesium. Electrolyte content from the 8 patches was similar among sites and ranged from 1.01–1.41 mg/d sodium, 0.35–0.83 mg/d potassium, 1.0– 1.45 mg/d calcium, and 0.43–0.49 mg/d magnesium. Projections from patches to whole body by the ratio of body surface area appear to overestimate actual whole body losses by 3.2X for sodium and calcium, 3.6X for magnesium, and 1.3X for potassium.

Conclusions:

Regional patch methods are more appropriate for relative comparisons than for accurately determining total daily dermal electrolyte losses.

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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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Ronald J. Maughan, Phillip Watson, Philip A.A. Cordery, Neil P. Walsh, Samuel J. Oliver, Alberto Dolci, Nidia Rodriguez-Sanchez and Stuart D.R. Galloway

) has recently been proposed to summarize such effects ( Maughan et al., 2016 ), and recently, it was demonstrated that body mass and sex do not influence the BHI ( Sollanek et al., 2018 ). Under resting euhydrated conditions, it appears that the carbohydrate, protein, and electrolyte content of

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Mindy L. Millard-Stafford, Phillip B. Sparling, Linda B. Rosskopf and Teresa K. Snow

Our purpose was to determine if sports drinks with 6 and 8% CHO differentially affect physiological responses or run performance in the heat. Ten men ran 32 km while ingesting: placebo (P), 6% carbohydrate-electrolyte (CE6), and 8% carbohydrate-electrolyte (CE8). At 15 km, a 250 mL drink labeled with deuterium oxide (D2O) was ingested. Blood glucose and respiratory exchange ratio were significantly higher (P < 0.05) for CE6 and CE8 compared to P. Rectal temperature (Tre) at 32 km was higher for CE8 (40.1 ± 0.2 °C) compared to P (39.5 ± 0.2 °C) but similar to CE6 (39.8 ± 0.2 °C). D2O accumulation was not different among drink trials. Run performance was 8% faster for CE8 (1062 ± 31 s) compared to P (1154 ± 56 s) and similar to CE6 (1078 ± 33 s). Confirming the ACSM Position Stand, 8% CE are acceptable during exercise in the heat and attenuate the decline in performance.

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Paola Rodriguez-Giustiniani, Ian Rollo, Oliver C. Witard and Stuart D. R. Galloway

, the primary aim of this study was to provide further practical insight into the influence of ingesting a 12% carbohydrate-electrolyte (CHO-E) beverage on soccer skill performance and high-intensity running capacity in professional youth academy soccer players. We hypothesized that ingesting 250 ml of

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Fred Brouns, Wim Saris and Heinz Schneider

The addition of carbohydrate and sodium to sport drinks has been recommended to enhance fluid intake and absorption and to delay fatigue. Other electrolytes (E) which are lost through sweating are also commonly added. However, too many E may lead to increased serum E and osmolality levels, which may negatively influence thermoregulation, depress sweating, and cause gastrointestinal distress. On the other hand, drinking large amounts of plain water to compensate sweat loss may induce hyponatremia. Therefore, literature describing sweat E losses was examined in order to estimate average whole-body E loss and to determine an upper limit for replacement of E with sport drinks. Mean E loss was determined from 13 studies, with +1 SD resulting in a hypothetical range for E losses. Correction for net absorption resulted in an upper limit of electrolyte replacement. It is suggested that the E levels in sport rehydration drinks should not exceed the upper limit of the range given.

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Yoram Epstein and Lawrence E. Armstrong

Body water and electrolyte balance are essential to optimal physiological function and health. During exercise, work, or high temperatures, a significant level of dehydration can develop, and the ratio of extracellular to intracellular fluid can change, despite an ample supply of water. Physical and cognitive performance are impaired at 1-2% dehydration, and the body can collapse when water loss approaches 7%. Because fluid needs and intakes vary, formulating one general guideline for fluid replacement is difficult. Knowing the amount of water lost in sweat may enable predicting fluid needs via mathematical models for industrial, athletic, and military scenarios. Sodium imbalance might result from excessive Na+ loss or from gross o verity dration. In most work or exercise lasting < 3-4 hr, the major concern is that fluid be available to prevent heat-related illnesses, which can be prevented if fluid and electrolyte losses are balanced with intake, using the recommendations presented.

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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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Lawrence E. Armstrong

Recreational enthusiasts and athletes often are advised to abstain from consuming caffeinated beverages (CB). The dual purposes of this review are to (a) critique controlled investigations regarding the effects of caffeine on dehydration and exercise performance, and (b) ascertain whether abstaining from CB is scientifically and physiologically justifiable. The literature indicates that caffeine consumption stimulates a mild diuresis similar to water, but there is no evidence of a fluid-electrolyte imbalance that is detrimental to exercise performance or health. Investigations comparing caffeine (100-680 mg) to water or placebo seldom found a statistical difference in urine volume. In the 10 studies reviewed, consumption of a CB resulted in 0-84% retention of the initial volume ingested, whereas consumption of water resulted in 0-81% retention. Further, tolerance to caffeine reduces the likelihood that a detrimental fluid-electrolyte imbalance will occur. The scientific literature suggests that athletes and recreational enthusiasts will not incur detrimental fluid-electrolyte imbalances if they consume CB in moderation and eat a typical U.S. diet. Sedentary members of the general public should be at less risk than athletes because their fluid losses via sweating are smaller.

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Oded Bar-Or and Boguslaw Wilk

This article reviews studies, mostly from the authors' laboratory, on children's sweating rates and composition, voluntary drinking patterns during prolonged exercise in the heat, taste perception of beverages, and the importance of fluid flavor and composition in preventing voluntary dehydration. Subjects were children, exposed for 90 to 180 min to intermittent bouts of cycling (45-50% maximal O2 uptake) in a climatic chamber (mostly at 35 C°, 40-50% relative humidity). There were five main findings: When given unflavored water ad libitum, children dehydrated progressively and their core temperature increased faster than in adults. When offered drinks with various flavors, children preferred grape to other flavors. When given grape-flavored water during intermittent exercise in the heat, children voluntarily drank 44.5% more than with unflavored water. When given grape-flavored carbohydrate-electrolyte solution, they voluntarily drank 91% more than with unflavored water. Finally, such consumption of carbohydrate-electrolyte solution was sufficient to prevent voluntary dehydration during 180-min intermittent exercise in the heat.