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THE JOURNAL OF SPORTS MEDICINE AND PHYSICAL FITNESS
Rivista di Medicina, Traumatologia e Psicologia dello Sport
Indexed/Abstracted in: Chemical Abstracts, CINAHL, Current Contents/Clinical Medicine, EMBASE, PubMed/MEDLINE, Science Citation Index Expanded (SciSearch), Scopus
Impact Factor 1,111
The Journal of Sports Medicine and Physical Fitness 1999 March;39(1):47-53
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
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.