Hydration assessment among marathoners using urine specific gravity and bioelectrical impedance analysis.

ABSTRACT

The present study examined the relationship between urine specific gravity (Usg), body mass (BM) and bioelectrical impedance determined variables [total body water (TBW), per cent TBW and impedance values] before and after a marathon (n = 25 men; 10 women). A significant reduction in BM (pre 71.2 ± 12.4 kg; post 69.6 ± 12.0 kg; p < 0.001) and an increase in Usg (pre 1.009 ± 0.007; post 1.018 ± 0.009; p < 0.001) was observed post-race. TBW was not significantly decreased (pre 42.7 ± 8.0 kg; post 42.4 ± 7.7 kg) while per cent TBW significantly increased post-race (pre 60.0 ± 3.9%; post 60.8 ± 3.8%; p < 0.001). Impedance values were significantly greater post-race (pre 3288 ± 482; post 3416 ± 492 Ω; p < 0.001). There was no correlation between the change in Usg and the change in BM or any of the bioelectrical impedance determined variables. On average, BM, Usg and impedance values appear to express changes in hydration; however, the observed changes among these variables for a given individual appear to be inconsistent with one another.