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The Acute Effects of Fluid Intake on Urine Specific Gravity and Fluid Retention in a Mildly Dehydrated State

Logan-Sprenger, Heather M.; Spriet, Lawrence L.

The Journal of Strength & Conditioning Research: April 2013 - Volume 27 - Issue 4 - p 1002–1008
doi: 10.1519/JSC.0b013e31826052c7
Original Research

Logan-Sprenger, HM and Spriet, LL. The acute effects of fluid intake on urine specific gravity and fluid retention in a mildly dehydrated state. J Strength Cond Res 27(4): 1002–1008, 2013—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.

Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada

Address correspondence to Heather M. Logan-Sprenger,

Copyright © 2013 by the National Strength & Conditioning Association.