EXAMINING URINE COLOR AS A MEASURE OF HYDRATION STATUS DURING MOUNTAIN BIKE RACES IN THE HEAT

Abstract

The purposes of this study were to examine a practical urine color index as a measure of hydration status during a field investigation and to substantiate previous laboratory findings. Following pre-exercise hydration (plain water) equal to 2.8% of body weight (to assure proper hydration before exercise), 12 heat-acclimated experienced male mountain bikers (age: 24.5 ± 1.1 years, % body fat: 14.3 ± 1.0%, weight: 76.9 ± 1.9 kg, height: 179 ± 2 cm) completed a 30 mile mountain bike race (finishing time = 158.0 ± 5.4 min) in the heat (WBGT = 82). The cyclists had no fluid during the entire ride. The riders stopped for 8 min following each 10 miles to collect data. % dehydrated (%DHY) was equivalent to the % of body weight lost. Urine specific gravity (USG) was measured with a refractometer with values from 1.000 to 1.035. The thirst scale (THIRST) was a subjective scale with descriptive words corresponding to numerical values ranging from 1 (not thirsty) to 9 (very, very, thirsty). The urine volume (UVOL) was the amount excreted since the previous measure. The urine color chart (UCOLOR) was a scale with colors corresponding to values ranging from 1 (very pale yellow) to 8 (brownish-green). The pre-exercise measures were done after sitting for 60 min without fluids.TableCorrelation's of UCOLOR with %DHY, USG, THIRST, and UVOL were .93, .92, .77, −.74, respectively (all p < .05). In summary, the data provide evidence that UCOLOR is a valid field tool to estimate the degree of dehydration. Additionally, they provide comparisons of UCOLOR with specific levels of dehydration.