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

Background. The aim of the study was to determine whether urine color, osmo lality and specific electrical conductance (SEC) provide an accurate index of hydration status and of fluid requirements during the recovery phase aft er an acute exercise-induced dehydration. Methods. Experimental design: eight well-trained healthy males were dehydra ted about 3% of body mass, 3 times, by cycling in the heat. To rehydrate af ter exercise, three types of drinks frequently consumed by athletes postexe rcise, i.e, a caffeinated soft drink (CC), a mineral water (MW), or a carbo hydrate-electrolyte solution (CES) were ingested ad libitum and in randomiz ed cross-over design during the first 2 hrs of an observation period lastin g 6 hrs, Measures: urine was sampled each hour for determination of color, osmolality and SEC. Net rehydration was calculated from fluid intake and fl uid 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 swea t. Urine output showed a negative correlation with color, osmolality and SE C (p<0.001), These variables were highly interrelated (p<0.001), However, t he 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 hydrati on status measured from the balance between fluid intake and urine output u p to 6 hrs postexercise.