IS URINE SPECIFIC GRAVITY A SATISFACTORY MEASURE OF HYDRATION STATUS?

1618 In 1998, to improve the safety of wrestling, the NCAA selected a urine specific gravity (Usg) of 1.020 as a limit for euhydration status. Wrestlers with Usg values exceeding 1.020 would not be allowed to have their body composition assessed to determine their minimum competitive wrestling weight for the season. The purposes of this investigation were to determine if: 1) a Usg of 1.020 represents a euhydration state, 2) a change in Usg correlates with a change in plasma osmolality (Posm), and if 3) Usg is a sensitive indicator of a change in hydration status. Euhydrated (Posm 288±4 mOsm) subjects (n=12) dehydrated by 5% of their body weight via exercise in a warm environment. Measurements of Posm, Uosm, and Usg were made at 1%, 3%, and 5% dehydration, and at 30 and 60 min of recovery. During recovery, subjects consumed a volume of water equal to the fluid volume lost by dehydration. (Table)TableUsg significantly correlated with Uosm (r=0.98), but poorly correlated with Posm (r=0.50). Usg was 1.021 at 5% dehydration and rose to 1.024 at 30 min recovery before declining to 1.020 at 60 min recovery. Posm correlated significantly with % weight loss (r=0.87). Based on these data, Usg is an unsatisfactory measure of hydration status; euhydrated wrestlers could lose 5% of body weight via dehydration and yet meet the Usg standard established by the NCAA. Supported by the National Collegiate Athletic Association.