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Accuracy of Urine Specific Gravity and Osmolality as Indicators of Hydration Status

Robert A. Oppliger, Scott A. Magnes, LeRoy A. Popowski, and Carl V. Gisolfi

To reduce the adverse consequences of exertion-related and acute intentional dehydration research has focused on monitoring hydration status. This investigation: 1) compared sensitivity of urine specific gravity (Usg), urine osmolality (Uosm) and a criterion measurement of hydration, plasma osmolality (Posm), at progressive stages of acute hypertonic dehydration and 2) using a medical decision model, determined whether Usg or Uosm accurately reflected hydra-tion status compared to Posm among 51 subjects tested throughout the day. Incremental changes in Posm were observed as subjects dehydrated by 5% of body weight and rehydrated while Usg and Uosm showed delayed dehydration-related changes. Using the medical decision model, sensitivity and specificity were not significant at selected cut-offs for Usg and Uosm. At the most accurate cut-off values, 1.015 and 1.020 for Usg and 700 mosm/kg and 800 mosm/kg for Uosm, only 65% of the athletes were correctly classified using Usg and 63% using Uosm. Posm, Usg, and Uosm appear sensitive to incremental changes in acute hypertonic dehydration, however, the misclassified outcomes for Usg and Uosm raise concerns. Research focused on elucidating the factors affecting accurate assessment of hydration status appears warranted.

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Relationship Between Changes in Upon-Waking Urinary Indices of Hydration Status and Body Mass in Adolescent Singaporean Athletes

Chin Han Lew, Gary Slater, Gobinathan Nair, and Michelle Miller

This study investigated the relationship between changes in upon-waking body mass (BM) and changes in urine specific gravity (Usg) and urine color (Ucol) from 1 day to the next. Throughout the 5-day investigation, healthy adolescent Singaporean athletes (n = 66) had their upon-waking, bladder-voided BM measured. A small aliquot of the first bladder void each day was collected and analyzed for Usg and Ucol, the latter by both an investigator (IUcol) and individual participants (SUcol). Results revealed a significant inverse relationship between changes in BM and changes in Usg (p = .003) and Ucol (p = .001). On average, Usg and Ucol changed by ~0.003 units and ~1 color (across a 9-unit scale), respectively, with every 1% change in BM from 1 day to the next. There was a stronger relationship between Usg and IUcol (r = .82, p < .001) than between Usg and SUcol (r = .60, p < .001). These results suggest that the degree of fluid deficit may be predicted from the Usg measurements among moderately hypohydrated athletes. In addition, training athletes to interpret and use the Ucol chart is recommended.

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A Review of Fluid and Hydration in Competitive Tennis

Mark S. Kovacs

Hypohydration is known to impair performance and increases the risk of heat injury. Therefore, the consumption of appropriate fluid volumes before, during, and after tennis play is important to maintain physiological homeostasis and performance. Tennis is a sport that typically has points lasting fewer than ten seconds, with short-to-moderate rest periods between each work bout. This sequence is repeated over hours. Most fuid and hydration research has focused on continuous aerobic exercise, which provides vastly different physiological strain compared with tennis practice and competition. Consequently, practical recommendations on maintaining hydration status for aerobic continuous exercise may not be appropriate for tennis athletes. Tennis players can sweat more than 2.5 L·h−1 and replace fluids at a slower rate during competition than in practice. In warm and hot environments, electrolyte-enhanced fluid should be consumed at greater than >200 mL per changeover and ideally closer to 400 mL per changeover. Tennis scientists, coaches, and players need to individualize hydration protocols to arrive at the optimal hydration strategy.

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Does Dehydration Affect the Adaptations of Plasma Volume, Heart Rate, Internal Body Temperature, and Sweat Rate During the Induction Phase of Heat Acclimation?

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

exacerbated in a dehydrated state. 10 Thus, euhydration (optimal hydration) and dehydration trials during heat acclimation induction have been conducted to determine if there are additional benefits to dehydrated exercise trials on plasma volume, heart rate, internal body temperature, skin temperature, and

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Changes of Hydration Measures in Elite National Collegiate Athletic Association Division I Wrestlers

Emily C. Borden, William J. Kraemer, Bryant J. Walrod, Emily M. Post, Lydia K. Caldwell, Matthew K. Beeler, William H. DuPont, John Paul Anders, Emily R. Martini, Jeff S. Volek, and Carl M. Maresh

. As noted previously, this may be a concern that, after the season, thirst sensation did not reflect the euhydration indicated in the urine and plasma biomarkers. When evaluated further, it was discovered that the individuals who perceived themselves most thirsty were indeed the most dehydrated at

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Hydration Marker Diagnostic Accuracy to Identify Mild Intracellular and Extracellular Dehydration

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

 al., 2008 ). Body mass loss was calculated on all trials to ensure euhydration was maintained on EU, and mild dehydration was achieved on ID and ED. A 1% threshold was used as this has previously been reported as the typical day-to-day variability of body mass in active men ( Cheuvront et al., 2010

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Variability of Body Mass and Urine Specific Gravity in Elite Male Field Hockey Players During a Pre-Olympic Training Camp

Jason D. Vescovi and Greig Watson

small meal (450 kcal) and 0.2 L of water or apple juice ( Cheuvront et al., 2010 ), compared with the field hockey players who consumed fluids and food ad libitum throughout the evening. The number of occurrences of euhydration and hypohydration the morning after matches was evenly distributed across

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Sports Dietitians Australia Position Statement: Nutrition for Exercise in Hot Environments

Alan J. McCubbin, Bethanie A. Allanson, Joanne N. Caldwell Odgers, Michelle M. Cort, Ricardo J.S. Costa, Gregory R. Cox, Siobhan T. Crawshay, Ben Desbrow, Eliza G. Freney, Stephanie K. Gaskell, David Hughes, Chris Irwin, Ollie Jay, Benita J. Lalor, Megan L.R. Ross, Gregory Shaw, Julien D. Périard, and Louise M. Burke

, or specific gravity); daily variation in body mass (BM); thirst; or ideally a combination of these ( Armstrong, 2007 ). Urinary markers reflect recent homeostatic processes to maintain euhydration and are not a direct assessment of hydration status itself. Therefore, urinary markers are likely to

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Nutrition for Ultramarathon Running: Trail, Track, and Road

Ricardo J.S. Costa, Beat Knechtle, Mark Tarnopolsky, and Martin D. Hoffman

, irrespective of humidity, requires an ability to maintain homeostatic core body temperature via thermoregulatory and/or cooling strategies (e.g., heat acclimatization/acclimation, internal cold fluid intake and/or external body cooling), and/or maintaining euhydration ( Brown & Connolly, 2015 ; Stevens et

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Hydration Status of Arabic Adolescents and Young Men: Measurement, Evaluation, and a School-Based Initiative to Improve Drinking Behavior

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


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


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).


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.


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.