Urine Specific Gravity and Osmolality Measurements in a College Football Team

Abstract

NCAA regulations prohibit wrestlers from competing when urine specific gravity (U) is >1.020 g/dL. To date, no other sport has been evaluated for acceptable hydration levels using this same criterion. PURPOSE: to assess the level of hydration in a college football team prior to fall training and after 8 weeks of competition using Usg, osomolality (Uosm), and dipsticks. METHODS: NCAA Division II football players (n = 78) provided a urine sample during their pre-season physical examination in early August (n = 78) and again in late October (n = 50). Prior to each sample collection, fluids and diet were allowed ad libitum. Players self-reported average daily fluid consumption in the six weeks preceding measurement. Usg was measured using a refractometer (ICAL model 2020) and dipsticks (Urispec 11-way), and U was determined using freezing-point depression (Advanced Micro-Osmometer, model 3300). RESULTS: Reliability determined on randomly selected subgroups (n = 20 and 18) produced interclass correlation coefficients of 0.999 for both Usg and Uosmat each test session. Usg and Uosm were highly correlated at both test sessions (r = 0.95 and 0.97). Dipstick U measurements were significantly lower than the refractometer levels (t = 8.7), despite a correlation between the two. At pre-season testing, 89% of the players had Usg above 1.020 g/dL, (p<0.01) while at late-season testing, 64% were above that level (p<0.01). The change between pre-season and late-season was significant. At both pre-season and late-season testing, self-reported water intake was nonsignificantly correlated with Usg (r = −0.03 and 0.04) and Uosm(r = −0.04 and 0.17). There was no significant difference in Usg orUosm between players using nutritional supplements and those not using any supplementation at either pre-season or late-season season. CONCLUSIONS: A large percentage of college football players may not be well hydrated entering pre-season training but are likely to become significantly better hydrated over the course a football season due to readily available water supplies during and after practice. Despite improved hydration status, a substantial percent of football players might not attain recommended hydration level (1.020g/dL).