Impact of Bolus versus Metered Fluid Consumption on Urine Specific Gravity and Urine Color

Abstract

PURPOSE: This study assessed urine specific gravity (USG) and urine color (UC) as measures of hydration status (compared to body mass changes) following bolus and metered rehydration. METHODS: Subjects (n=8) exercised in a climate controlled chamber (35°C, 55% RH) until a 2% loss of body weight was obtained. In 4 separate trials, fluids (water and a carbohydrate-electrolyte beverage) were replaced using bolus (100% volume replacement within 1hr) and metered (12.5% of total volume every 30 minutes for 4 hrs) administrations. Urine was collected as produced for 8 hours following dehydration. USG, UC, and urine volumes were measured for each void. RESULTS: Pearson and Spearman correlations revealed weak relationships (r = 0.01 to r = 0.34) between changes in % hydration measured by body weight and USG, and UC, regardless of administration techniques or recovery beverages used; however, correlations between USG and UC varied from r = 0.63 to 0.86. CONCLUSIONS: Whereas changes in USG and UC tracked well with one another, these data suggest that these urinary markers may be limited in value when used to track hydration status in less than 2% hypohydrated healthy ambulatory people.