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.
Robert A. Oppliger, Scott A. Magnes, LeRoy A. Popowski and Carl V. Gisolfi
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.
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.
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
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
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
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
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.
Joseph F. Seay, Brett R. Ely, Robert W. Kenefick, Shane G. Sauer and Samuel N. Cheuvront
We examined the effect of body water deficits on standing balance and sought to determine if plasma hyperosmolality (Posm) and/or volume reduction (%ΔVplasma) exerted independent effects. Nine healthy volunteers completed three experimental trials which consisted of a euhydration (EUH) balance test, a water deficit session and a hypohydration (HYP) balance test. Hypohydration was achieved both by exercise-heat stress to 3% and 5% body mass loss (BML), and by a diuretic to 3% BML. Standing balance was assessed during quiet standing on a force platform with eyes open and closed. With eyes closed, hypohydration significantly decreased medial-lateral sway path and velocity by 13% (both p < .040). However, 95% confidence intervals for the mean difference between EUH and HYP were all within the coefficient of variation of EUH measures, indicating limited practical importance. Neither Vplasma loss nor Posm increases were associated with changes in balance. We concluded that standing balance was not altered by hypohydration.
Lawrence E. Armstrong, Amy C. Pumerantz, Kelly A. Fiala, Melissa W. Roti, Stavros A. Kavouras, Douglas J. Casa and Carl M. Maresh
It is difficult to describe hydration status and hydration extremes because fluid intakes and excretion patterns of free-living individuals are poorly documented and regulation of human water balance is complex and dynamic. This investigation provided reference values for euhydration (i.e., body mass, daily fluid intake, serum osmolality; M ± SD); it also compared urinary indices in initial morning samples and 24-hr collections. Five observations of 59 healthy, active men (age 22 ± 3 yr, body mass 75.1 ± 7.9 kg) occurred during a 12-d period. Participants maintained detailed records of daily food and fluid intake and exercise. Results indicated that the mean total fluid intake in beverages, pure water, and solid foods was >2.1 L/24 hr (range 1.382–3.261, 95% confidence interval 0.970–3.778 L/24 hr); mean urine volume was >1.3 L/24 hr (0.875–2.250 and 0.675–3.000 L/24 hr); mean urine specific gravity was >1.018 (1.011–1.027 and 1.009–1.030); and mean urine color was ≥4 (4–6 and 2–7). However, these men rarely (0–2% of measurements) achieved a urine specific gravity below 1.010 or color of 1. The first morning urine sample was more concentrated than the 24-h urine collection, likely because fluids were not consumed overnight. Furthermore, urine specific gravity and osmolality were strongly correlated (r2 = .81–.91, p < .001) in both morning and 24-hr collections. These findings provide euhydration reference values and hydration extremes for 7 commonly used indices in free-living, healthy, active men who were not exercising in a hot environment or training strenuously.