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James M. Carter, Tom Loney, Sam D. Blacker, Graham F. Nicholson and David M. Wilkinson

Background:

Despite the importance of hydration, limited research on the topic has been undertaken in Arabic populations.

Methods:

Study 1. Five sequential daily midmorning urine samples were provided by 88 adult military cadets and 32 school-based adolescents. Hydration thresholds were produced using percentiles of estimated urine osmolality (Uosm) and urine color (Ucol). Study 2. The authors assessed 1,077 midmorning urine samples from 120 military cadets and 52 adolescents for the Uosm:Ucol relationship using regression. Study 3. The authors conducted a 4-wk hydration campaign in which 21 adolescents participated, providing urine samples before (PreC), at the end of (EndC), and 2 wk after the campaign (PostC).

Results:

Study 1. Euhydration (41–60th percentile) was 881–970 mOsmol/kg in adults and 821–900 mOsmol/kg in adolescents. Study 2. In both cohorts, Uosm and Ucol were associated (p < .01): adults R 2 = .33, adolescents R 2 = .59. Study 3. Urine osmolality was significantly higher PreC than at EndC and PostC.

Conclusions:

Urinary output of Arabic adolescents and military cadets was more concentrated than frequently recommended for euhydration. Further work in similar populations is required to determine if these values represent hypohydration or merely reflect dietary and cultural differences. In male Arabic adolescents and adults, Ucol was an adequate indicator of hydration status. Favorable hydration changes were made after a school-based health campaign.

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Daniel J. Peart, Andy Hensby and Matthew P. Shaw

The purpose of this study was to compare markers of hydration during submaximal exercise and subsequent time trial performance when consuming water (PW) or coconut water (CW). There was also a secondary aim to assess the palatability of CW during exercise and voluntary intake during intense exercise. 10 males (age 27.9 ± 4.9 years, body mass 78.1 ± 10.1kg, average max minute power 300.2 ± 28.2W) completed 60-min of submaximal cycling followed by a 10-km time trial on two occasions. During these trials participants consumed either PW or CW in a randomized manner, drinking a 250 ml of the assigned drink between 10–15 min, 25–30 min and 40–45 min, and then drinking ad libitum from 55-min until the end of the time trial. Body mass and urine osmolality were recorded preexercise and then after 30-min, 60-min, and post time trial. Blood glucose, lactate, heart rate, rate of perceived exertion (RPE; 6–20) and ratings of thirst, sweetness, nausea, fullness and stomach upset (1 =very low/none, 5= very high) were recorded during each drink period. CW did not significantly improve time trial performance compared with PW (971.4 ± 50.5 and 966.6 ± 44.8 s respectively; p = .698) and there was also no significant differences between trials for any of the physiological variables measured. However there were subjective differences between the beverages for taste, resulting in a significantly reduced volume of voluntary intake in the CW trial (115 ± 95.41 ml and 208.7 ± 86.22 ml; p < .001).

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Nora R. Decher, Douglas J. Casa, Susan W. Yeargin, Matthew S. Ganio, Michelle L. Levreault, Catie L. Dann, Camille T. James, Megan A. McCaffrey, Caitlin B. O’Connor and Scott W. Brown

Purpose:

To assess the hydration status and level of hydration knowledge of youths at summer sports camps.

Methods:

Sixty-seven active youths, 57 males (mean ± SD, 12 ± 2 y, 136 ± 16 cm, 50.6 ± 21.1 kg) and 10 females (13 ± 2 y, 153 ± 8 cm, 45.2 ± 9.0 kg) participated in 4 d of sports camp. Hydration status was assessed before the first practice (AM) and after the second practice (PM). Participants completed suriveys assessing hydration knowledge (HAQ) and hydration habits on day 3 and a self-assessment (EQ#1).

Results:

Mean AM urine specific gravity (USG) and urine osmolality (Uosm) scores ranged from minimal to significant dehydration across 4 d, even when temperatures were mild. Correlations between hydration indices and EQ#1, ranging from 0.11 to −0.51, were statistically significant (P < .05), indicating that subjects recognized when they were doing a good or bad job hydrating. HAQ did not correlate strongly with hydration indices suggesting other impediments to hydration. Thirst correlated negatively with EQ#1 (from −0.29 to −0.60).

Conclusion:

Hydration at summer sports camp is a concern and special efforts need to be made to help youths develop hydration strategies.

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Lawrence E. Armstrong, Carl M. Maresh, John W. Castellani, Michael F. Bergeron, Robert W. Kenefick, Kent E. LaGasse and Deborah Riebe

Athletes and researchers could benefit from a simple and universally accepted technique to determine whether humans are well-hydrated, euhydrated, or hypohydrated. Two laboratory studies (A, B) and one field study (C) were conducted to determine if urine color (Ucol) indicates hydration status accurately and to clarify the interchangeability of Ucol, urine osmolality (Uosm), and urine specific gravity (Usg) in research. Ucol, Uosm, and Usg were not significantly correlated with plasma osmolality, plasma sodium, or hemato-crit. This suggested that these hematologic measurements are not as sensitive to mild hypohydration (between days) as the selected urinary indices are. When the data from A, B, and C were combined, Ucol was strongly correlated with Uhg and U„sm. It was concluded that (a) Ucol may be used in athletic/industrial settings or field studies, where close estimates of Usg or Uosm are acceptable, but should not be utilized in laboratories where greater precision and accuracy are required, and (b) Uosm and Usg may be used interchangeably to determine hydration status.

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Samuel N. Cheuvront, Robert W. Kenefick and Edward J. Zambraski

A common practice in sports science is to assess hydration status using the concentration of a single spot urine collection taken at any time of day for comparison against concentration (specific gravity, osmolality, color) thresholds established from first morning voids. There is strong evidence that this practice can be confounded by fluid intake, diet, and exercise, among other factors, leading to false positive/negative assessments. Thus, the purpose of this paper is to provide a simple explanation as to why this practice leads to erroneous conclusions and should be curtailed in favor of consensus hydration assessment recommendations.

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Craig A. Williams and Jamie Blackwell

The purpose of the study was to determine the hydration status, fluid intake, and electrolyte losses of 21 male professional youth soccer players (age 17.1 ± 0.7 y) training in a cool environment. Pretraining and posttraining measurements of body mass, urine (freezing-point osmolality method), and sweat concentration (flame-emission spectroscopy) were collected. Fourteen players were found to be hypohydrated before training. The amount of fluid lost due to exercise equated to a 1.7% loss in body mass, which equated to a gross dehydration loss of 0.5%. Overall, the soccer players replaced 46% ± 88% of sweat loss during training, and only 4 remained hypohydrated after training. No significant correlations between sweat loss and sweat concentrations of Na+ (r = –.11, P = .67) or K+ (r = .14, P = .58) were found, but there was a significant correlation with Mg2+ (r = –.58, P < .009). This study found large variability in pretraining hydration status that the players were able to rehydrate during the training sessions. However, given the numbers starting training in a hypohydrated state, adequate hydration status before training should be considered by youth players, coaches, and sports-science support staff.

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Julian A. Owen, Matthew B. Fortes, Saeed Ur Rahman, Mahdi Jibani, Neil P. Walsh and Samuel J. Oliver

immediately analyzed for urine color by an 8-point chart ( Armstrong et al., 1994 ), urine specific gravity was measured in duplicate using a handheld refractometer (Atago, Tokyo, Japan), and urine osmolality was measured in triplicate by a freezing point depression osmometer (model 3300; Advanced Instruments

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J.D. Adams, Stavros A. Kavouras, Evan C. Johnson, Lisa T. Jansen, Catalina Capitan-Jimenez, Joseph I. Robillard and Andy Mauromoustakos

The purpose of this investigation was to quantify the effects of storage temperature, duration, and the urinary sediment on urinary hydration markers. Thirty-six human urine samples were analyzed fresh and then the remaining sample was separated into 24 separate vials, six in each of the following four temperatures: 22 °C, 7 °C, -20 °C, and -80 °C. Two of each sample stored in any given temperature, were analyzed after 1, 2, and 7 days either following vortexing or centrifugation. Each urine sample was analyzed for osmolality (UOsm), urine specific gravity (USG), and urine color (UC). UOsm was stable at 22 °C, for 1 day (+5–9 mmol∙kg-1, p > .05) and at 7 °C, UOsm up to 7 days (+8–8 mmol∙kg-1, p > .05). At -20 and -80 °C, UOsm decreased after 1, 2, and 7 days (9–61 mmol∙kg-1, p < .05). Vortexing the sample before analysis further decreased only UOsm in the -20 °C and -80 °C storage. USG remained stable up to 7 days when samples were stored in 22 °C or 7 °C (p > .05) but declined significantly when stored in -20 °C, and -80 °C (p < .001). UC was not stable in any of the storing conditions for 1, 2, and 7 days. In conclusion, these data indicate that urine specimens analyzed for UOsm or USG remained stable in refrigerated (7 °C) environment for up to 7 days, and in room temperature for 1 day. However, freezing (-20 and -80 °C) samples significantly decreased the values of hydration markers.

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Paola Rodriguez-Giustiniani and Stuart D.R. Galloway

osmolality and sodium and potassium concentrations. Duplicate measurements of serum and urine osmolality were made using the freezing-point depression method (Löser Micro-Digital Osmometer M15, Berlin, Germany). Sodium and potassium of urine, sweat, and drink samples were determined in duplicate by flame

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Damir Zubac, Drazen Cular and Uros Marusic

boxers in particular) are at greater risk of serious hypohydration than other combat athletes, mainly due to shorter recovery time between official weigh-in and the beginning of competition. 7 Although U SG and urine osmolality (U OSM ) were suggested as the most commonly used dehydration markers among