Background: Mean daily water intake from fluids (WATER-FL) has proven to be difficult to measure because of a range of nonvalidated data collection t

The purpose of this investigation was to quantify the effects of storage temperature, duration, and the urinary sediment on urinary hydration markers. Thirty-six human urine samples were analyzed fresh and then the remaining sample was separated into 24 separate vials, six in each of the following four temperatures: 22 °C, 7 °C, -20 °C, and -80 °C. Two of each sample stored in any given temperature, were analyzed after 1, 2, and 7 days either following vortexing or centrifugation. Each urine sample was analyzed for osmolality (UOsm), urine specific gravity (USG), and urine color (UC). UOsm was stable at 22 °C, for 1 day (+5–9 mmol∙kg-1, p > .05) and at 7 °C, UOsm up to 7 days (+8–8 mmol∙kg-1, p > .05). At -20 and -80 °C, UOsm decreased after 1, 2, and 7 days (9–61 mmol∙kg-1, p < .05). Vortexing the sample before analysis further decreased only UOsm in the -20 °C and -80 °C storage. USG remained stable up to 7 days when samples were stored in 22 °C or 7 °C (p > .05) but declined significantly when stored in -20 °C, and -80 °C (p < .001). UC was not stable in any of the storing conditions for 1, 2, and 7 days. In conclusion, these data indicate that urine specimens analyzed for UOsm or USG remained stable in refrigerated (7 °C) environment for up to 7 days, and in room temperature for 1 day. However, freezing (-20 and -80 °C) samples significantly decreased the values of hydration markers.

Post-exercise rehydration has been widely studied, with particular emphasis on retention of ingested fluid; comparatively little research has been conducted on why we drink more or less. To identify physiological values corresponding to voluntary drinking cessation (VDC), nine males exercised intermittently at 70–80% HRmax in the heat (WBGT = 28.1 ± 0.7 °C) to achieve a dehydration of approximately 4.0% body mass (BM). After exercise, participants were instructed to drink water as long and as much as they needed. Urine color (U_color), specific gravity (USG), osmolality (U_osm), plasma osmolality (P_osm), fullness, BM, and thirst perception (TP) were measured pre- and post-exercise and at VDC. Each variable was compared for the three points in time with a one-way ANOVA. Participants reached dehydration of −3.6 ± 0.3% BM. Pre-exercise USG (1.022 ± 0.004) was lower than at VDC (1.029 ± 0.004, p = 0.022), U_osm did not change over time (p = 0.217), and U_color was lower pre-exercise (3.4 ± 0.7) vs. post-exercise (5.5 ± 1.23, p = 0.0008) and vs. VDC (6.3 ± 1.1, p < 0.0001). P_osm showed a difference between pre-exercise (289.5 ± 2.3) and post-exercise (297.8 ± 3.9, p = 0.0006) and between post-exercise and VDC (287.3 ± 5.4, p < 0.0001). TP post-exercise (96.4 ± 4.34) was significantly higher than pre-exercise (36.2 ± 19.1) and VDC (25.0 ± 18.2, p < 0.0001). At VDC, participants had recovered 58.7 ± 12.1% of BM loss. At the point of voluntary drinking cessation, P_osm and thirst perception had returned to their pre-exercise values, while rehydration relative to initial BM was still incomplete.

Background: Thirst has been used as an indicator of dehydration; however, as a perception, we hypothesized that it could be affected by received information related to fluid losses. The purpose of this study was to identify whether awareness of water loss can impact thirst perception during exercise in the heat. Methods: Eleven males participated in two sessions in random order, receiving true or false information about their fluid losses every 30 min. Thirst perception (TP), actual dehydration, stomach fullness, and heat perception were measured every 30 min during intermittent exercise until dehydrated by ~4% body mass (BM). Post exercise, they ingested water ad libitum for 30 min. Results: Pre-exercise BM, TP, and hydration status were not different between sessions (p > 0.05). As dehydration progressed during exercise, TP increased significantly (p = 0.001), but it was the same for both sessions (p = 0.447). Post-exercise water ingestion was almost identical (p = 0.949) in the two sessions. Conclusion: In this study, thirst was a good indicator of fluid needs during exercise in the heat when no fluid was ingested, regardless of receiving true or false water loss information.

Este estudio experimental fue diseñado para evaluar durante el ejercicio y la rehidratación ad libitum post-ejercicio, si las percepciones subjetivas de sed y calor, así como la ingesta voluntaria de agua, son distintas en dos condiciones ambientales diferentes pero equivalentes en cuanto al índice de estrés térmico. Métodos: 14 participantes se ejercitaron en dos ocasiones en un cuarto de clima controlado (WBGT≈28.5° C): una vez para el calor seco (SECO, TBS = 33.8°C, HR = 53%) y una para el calor húmedo (HUM, TBS = 32.1°C y HR = 67%) sin ingesta de fluidos, hasta alcanzar una deshidratación equivalente al 4% MC. Las percepciones de sed, calor, llenura y cólico se midieron cada 30 min durante el ejercicio. Posteriormente ingirieron agua ad libitum durante 90 minutos. También se midió la ingesta voluntaria de agua. Resultados: Durante el ejercicio, la percepción de sed fue la misma para ambas condiciones (SECO 64.44±23.38, HUM 67.32±20.41mm; p=0.409), pero aumentó con el tiempo (p = 0.0001). Lo mismo ocurrió con la percepción de calor: no hubo diferencia entre las condiciones (SECO 6.34±0.50, HUM 6.40±0.37ua; p=0.423), pero aumentó a través del tiempo (p=0.001). Al final de la rehidratación, la percepción de calor fue mayor para el calor seco (5.3 ± 0.2ua) que para el calor húmedo (4.7 ± 0.2ua, p=0.006). La sed al final del ejercicio (85.8 ± 19.4mm) no mostró correlación significativa con la deshidratación real (3.82 ± 0.18% MC, r = -0.14, p = 0.48) ni con el consumo voluntario de agua (1843 ± 587 mL, r = -0.04, p = 0.85). No hubo correlación entre la pérdida de sudor real (2766 ± 700 ml) y la ingesta voluntaria de agua (r = 0.16, p = 0.42). La asociación entre el balance neto de fluidos y la percepción de la sed fue de R²_a= 0.70 (p = 0.001) Conclusiones: la percepción de sed y calor fue la misma cuando se realizó ejercicio en dos condiciones ambientales diferentes con el mismo nivel de estrés térmico. La escala de percepción de la sed fue capaz de detectar la deshidratación progresiva consistentemente: cuanto mayor fue la deshidratación en el tiempo, mayor fue la sed. Sin embargo, los resultados de este estudio no apoyan la teoría de que la ingesta voluntaria de agua es adecuada para reponer las pérdidas de sudor después del ejercicio.