Despite availability of a wide variety of methods to assess hydration and dehydration, researchers and practitioners are still looking for a practical, reliable method to assess acute hydration status.
PURPOSE: To measure the time course of urine volume discarded in response to ingesting a standard volume of water at different levels of dehydration, in an attempt to develop a practical method to assess acute hydration status in individuals.
METHODS: Nine healthy, physically active males, aged 23.5 ± 2.6 years old (mean ± standard deviation) reported to the laboratory after an overnight fast of 10 hours or more. Participants exercised intermittently in an environmental chamber (average temperature and relative humidity = 32°C and 65%, respectively) until dehydrated to 0, 1, 2 or 3% BM on different days; the order of treatments was randomized. Upon reaching the desired dehydration, they ingested a volume of water equivalent to 1.43% BM in 30 minutes. At the end of the rehydration period, participants voided and the urine was discarded (time 0); urine was collected henceforth every 30 minutes for 5 hours.
RESULTS: Collected urine volumes were larger for 0% BM (1236.8 ± 489.4 mL) than the other conditions (375.3 ± 170.2 mL, 235.9 ± 66.0 mL, and 261.7 ± 51.8 mL for 1, 2, and 3% BM, respectively) (p = 0.001), but there were no statistically significant differences among the latter three (p > 0.05). The cumulative volume differences between 0% BM and the rest of the treatments were significant at time = 60 min (p < 0.05) and remained significant for the remainder of the test. Average volumes (95% CI) for 0, 1, 2, and 3% BM at 60 min were: 652.8 mL (367.6 to 937.9 mL), 145.0 mL (97.3 to 192.7 mL), 80.9 mL (56.3 to 105.4 mL), and 100.2 mL (74.1 to 126.3 mL), respectively.
CONCLUSIONS: this method allows for a practical verification of an individual's acute hydration status, giving him/her a volume equivalent to 1.43%BM and collecting urine for 60 minutes; if the individual discards less than 367 mL in that time, he/she is hypohydrated.
