The acute effects of fluid intake on urine specific gravity and fluid retention in a mildly dehydrated state.

ABSTRACT

Many athletes arrive at training sessions and competitions in a mildly hypohydrated (HYPO) state and are instructed to drink fluids before exercise to reach a euhydrated (HYD) state. Ten recreational athletes (6 women, 4 men; 71.9 ± 4.6 kg, 25.2 ± 0.9 years) participated in the studies to examine (a) the day-to-day variability of morning urine specific gravity (USG), (b) the effects of consuming 600 ml of water on the hydration status of HYD and HYPO (USG > 1.020) subjects, and (c) the effects of consuming water (W), salt-water (SW, 40 mM Na), a carbohydrate-electrolyte solution with 3% or light carbohydrate (CES-L, 20 mM Na) or a CES with 6% carbohydrate (CES, 20 mM Na) on the hydration status of HYPO subjects. The hydration status was assessed with USG and body mass measures and urine volume collections. The day-to-day variability in morning USG (coefficient of variation = 0.2 ± 0.1%) was low and the responses to 600 ml of W ingestion were repeatable. Pretrial USG was 1.022 ± 0.001 in the HYPO trial and decreased <1.020 by 45 minutes (1.013 ± 0.003). In the CES study, HYPO subjects reached HYD status at 45 minutes in all conditions (W 1.013 ± 0.003, SW 1.013 ± 0.003, CES-L 1.011 ± 0.003, CES 1.017 ± 0.004) because salt or CES ingestion did not affect fluid retention (W 68%, SW 72%, CES-L 68%, CES 76%). This study demonstrated that mildly HYPO subjects could reach euhydration within 45 minutes of the ingestion of 600 ml of W or a combination of salt and CES solutions. Following this practice will minimize the incidence of starting a practice or competition hypohydrated.