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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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Andreas M. Kasper, Ben Crighton, Carl Langan-Evans, Philip Riley, Asheesh Sharma, Graeme L. Close and James P. Morton

in body mass (i.e., 3.7%), daily urine output (e.g., an increase of 150% from 4 to 6 L), and plasma sodium concentrations (maintained within the range of 136–140 mmol/L) to that observed by the previous authors. When taken together, such data suggest that the water-loading protocol reported here and

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Mark A. Tarnopolsky, Kerry Dyson, Stephanie A. Atkinson, Duncan MacDougall and Cynthia Cupido

We studied the effects of different CHO supplements on exercise metabolism (1 hr at 75% V˙O2) and performance (fatigue time at 85% V˙O2) in 8 male endurance athletes (VO2max=68.8±3.8 mlkg1min1) Four treatments were administered in a randomized, double-blind fashion: Trial A = 3-day pretest, postexercise supplementation (177 kcal [81% carbohydrate, 19% protein] consumed < 10 min after exercise) + 600 ml 8% glucose polymers/ fructose 1 hr pretesting + 600 ml 8% glucose polymers/glucose during testing; Trial B = placebo during 3-day pretest + remainder same as Trial A; Trial C = placebo at all time points; and Trial D = same as Trial B with 8% glucose 1 hr before the test as well as during the test. Time to fatigue at 85% V˙O2max (Í24%) and total CHO oxidation were greater for A versus C (p < .05). Plasma glucose concentration was higher for A and B versus C, while increases in plasma potassium concentration were attenuated for A versus C (both p < .05). None of the supplements had differential effects upon hematocrit, plasma sodium [Na+] and lactate, V˙O2, or rating of perceived exertion during exercise. Three-day preexercise protein + carbohydrate supplements followed by 1-hr pre- and during-exercise mixed carbohydrate supplements increased time to fatigue and carbohydrate oxidation and attenuated rises in plasma [K+] com pared to placebo.

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Asma Aloui, Anis Chaouachi, Hamdi Chtourou, Del P. Wong, Monoem Haddad, Karim Chamari and Nizar Souissi

Purpose:

This study examined the effects of Ramadan on cycling repeated-sprint ability (RSA) and corresponding diurnal variations.

Methods:

Twelve active men performed an RSA test (5 × 6-s maximal sprints interspersed with 24 s passive recovery) during morning and afternoon sessions 1 wk before Ramadan (BR), during the second (R2) and the fourth (R4) weeks of Ramadan, and 2 wk after Ramadan (AR). Maximal voluntary contraction was assessed before (MVCpre), immediately after (MVCpost), and 5 min after the RSA test (MVCpost5). Moreover, hematocrit, hemoglobin, and plasma sodium and potassium (K+) concentrations were measured at rest and after the RSA test and MVCpost.

Results:

Overall, peak power (Ppeak) during the RSA test decreased throughout the 5 sprints. Ppeak measured in the first sprint and MVCpre were lower during Ramadan than BR in the afternoon (P < .05) and higher in the afternoon than the morning BR and AR (P < .05). However, this diurnal rhythmicity was not found for the last 4 sprints’ Ppeak, MVCpost, and MVCpost5 in all testing periods. Furthermore, the last 4 sprints’ Ppeak, MVCpost, MVCpost5, and morning MVCpre were not affected by Ramadan. [K+] measured at rest and after the RSA test and MVCpost were higher during Ramadan than BR in the afternoon (P < .05) and higher in the afternoon than the morning during Ramadan (P < .05).

Conclusions:

Fatigability is higher in the afternoon during Ramadan, and, therefore, training and competition should be scheduled at the time of day when physical performance is less affected.

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Lawrence E. Armstrong, Jorge A. Herrera Soto, Frank T. Hacker Jr., Douglas J. Casa, Stavros A. Kavouras and Carl M. Maresh

This investigation evaluated the validity and sensitivity of urine color (Ucol), specific gravity (Usg), and osmolality (Uosm) as indices of hydration status, by comparing them to changes in body water. Nine highly trained males underwent a 42-hr protocol involving dehydration to 3.7% of body mass (Day 1, −2.64 kg), cycling to exhaustion (Day 2, −5.2% of body mass, −3.68 kg), and oral rehydration for 21 hr. The ranges of mean (across time) blood and urine values were Ucol, 1-7; Usg, 1.004-1.029; U08m, 117-1,081 mOsm • kg−1; and plasma osmolality (Posm), 280-298 mOsm ⋅ kg−1. Urine color tracked changes in body water as effectively as (or better than) Uosm, Usg, urine volume, Posm, plasma sodium, and plasma total protein. We concluded that (a) Ucol, Uosm, and Usg are valid indices of hydration status, and (b) marked dehydration, exercise, and rehydration had little effect on the validity and sensitivity of these indices.

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Rachel Lohman, Amelia Carr and Dominique Condo

, E. , Franken , C. , Cotter , J. , Thornton , S. , & Rehrer , N. ( 2017 ). Restricting dietary sodium reduces plasma sodium response to exercise in the heat . Scandinavian Journal of Medicine & Science in Sports, 27 ( 11 ), 1213 – 1220 . PubMed ID: 27714955 doi:10.1111/sms.12748 10

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Alan J. McCubbin, Gregory R. Cox and Ricardo J.S. Costa

Journal of Sports Medicine, 49 ( 22 ), 1432 – 1446 . PubMed ID: 26227507 doi:10.1136/bjsports-2015-095004 10.1136/bjsports-2015-095004 Hew-Butler , T. , Stuempfle , K.J. , & Hoffman , M.D. ( 2013 ). Bone: An acute buffer of plasma sodium during exhaustive exercise? Hormone and Metabolic

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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

equipment Blood sample and resources required (cost, equipment, and expertise) Plasma sodium concentration Ion-selective electrode a Direct measure and common clinical laboratory measure Blood sample and resources required (cost, equipment, and expertise) a Reference method of assessment. Changes in TBW