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The Journal of Sports Medicine and Physical Fitness 1999 March;39(1):47-53

language: English

Urine col­or, osmo­lal­ity and spe­cif­ic electri­cal con­duc­tance are not accu­rate meas­ures of hydra­tion stat­us dur­ing ­postexer­cise rehy­dra­tion

Kovacs E. M. R. 1, Senden J. M. G. 1, Brouns F. 2

1 Department of Human Biology, Maastricht University;
2 Novartis Nutrition Research Unit, Maastricht, The Netherlands


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Background. The aim of the ­study was to deter­mine wheth­er ­urine col­or, osmo­lal­ity and spe­cif­ic electri­cal con­duc­tance (SEC) pro­vide an accu­rate ­index of hydra­tion stat­us and of ­fluid require­ments dur­ing the recov­ery ­phase ­after an ­acute exer­cise-­induced dehy­dra­tion.
Methods. Experimental ­design: eight ­well-­trained ­healthy ­males ­were dehy­drat­ed ­about 3% of ­body ­mass, 3 ­times, by ­cycling in the ­heat. To rehy­drate ­after exer­cise, ­three ­types of ­drinks fre­quent­ly con­sumed by ath­letes ­postexer­cise, i.e. a caf­fei­nat­ed ­soft ­drink (CC), a min­er­al ­water (MW), or a car­bo­hy­drate-elec­tro­lyte solu­tion (CES) ­were ingest­ed ad lib­it­um and in ran­dom­ized ­cross-­over ­design dur­ing the ­first 2 hrs of an obser­va­tion peri­od last­ing 6 hrs. Measures: urine was sam­pled ­each ­hour for deter­mi­na­tion of col­or, osmo­lal­ity and SEC. Net rehy­dra­tion was cal­cu­lat­ed ­from ­fluid ­intake and ­fluid ­loss by ­sweat and ­urine.
Results. Fluid ­intake amount­ed 2.6±0.2 kg for CC, 2.2±0.2 kg for MW and 2.8±0.3 kg for CES rep­re­sent­ing 116%, 96% and 127% of ­fluid ­lost by ­sweat. Urine out­put ­showed a neg­a­tive cor­re­la­tion ­with col­or, osmo­lal­ity and SEC (p<0.001). These var­i­ables ­were high­ly inter­re­lat­ed (p<0.001). However, the lev­el of rehy­dra­tion did not cor­re­late ­with any of the meas­ured uri­nary var­i­ables (p>0.05).
Conclusions. Urine col­or, SEC and osmo­lal­ity are ­poor indi­ca­tors of hydra­tion stat­us meas­ured ­from the bal­ance ­between ­fluid ­intake and ­urine out­put up to 6 hrs ­postexer­cise.

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