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Smith, A.E., B. S. Roberts, A. Koch, and J. Mayhew . Missouri Journal of Health, Physical Education, Recreation & Dance 16:38-47, 2006.
NCAA regulations prohibit wrestlers from competing when urine specific gravity (Usg) is >1.020. The assessment of Usg is usually performed on a single occasion typically during the afternoon hours. Despite the finality of the measurement for determining wrestling eligibility, no evaluation of the within-and between-day variability of measurement has been done. The purpose of this study was to assess the variations in measurement of U<sub>sg</sub> and osomolality (Uosm within and between days. Six moderately trained individuals (5 M, 1 F) collected 138 samples over a 5-day period. Fluids and diet were allowed ad libitum. Usg was measured in duplicate using a refractometer (ICAL model 2020), and Uosm was determined using freezing-point depression (Advanced Micro-Osmometer, model 3300). The interclass correlation coefficients were ICC = 0.99 for both Usg and Uosm. Usg was highly correlated with Uosm (r = 0.98) indicating that a Uosm = 755 mOsm was equivalent to a Usg = 1.020. Individual within-day variations ranged from 0.0069 to 0.0084 for Usg and 279 to 323 for Uosm. Individual between-day variation ranged from 0.0016 to 0.0084 for Usg and 133 to 354 for Uosm. Repeated-measures ANOVA across days indicated no significant pattern to either Usg or Uosm. Fifty-eight samples (44%) were above the 1.020 cut-off and ranged from 2% to 92% within individuals. Daily water intake was significantly inversely correlated with Usg (r = -0.43) or Uosm (r = -0.38). Use of protein supplements was significantly directly correlated with Usg (r = 0.68) or Uosm (r = 0.70). Time of day does not appear to be an essential criteria for assessing Usg and Uosm. However, water intake and/or protein supplementation may increase both the within-day and between-day variations of measurement.
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