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C-31 Free Communication/Poster - Hydration and Fluid Balance in Sport: MAY 31, 2007 7: 30 AM - 12: 30 PM ROOM: Hall E

Initial Hydration Status and Fluid Balance during Recreational Exercise in Physically Active Adults

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Board #153 May 31 8:00 AM - 9:30 AM

Peacock, Oliver J.; Stokes, Keith A.; Thompson, Dylan

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Medicine & Science in Sports & Exercise: May 2007 - Volume 39 - Issue 5 - p S315
doi: 10.1249/01.mss.0000274224.87647.70
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Athletes typically fail to consume sufficient fluids during exercise to replace losses, whilst many arrive for exercise already dehydrated. However, very little is known about the pre-exercise hydration status and fluid balance of recreational exercisers, which may influence exercise adherence and overall wellbeing.

PURPOSE: To investigate initial hydration status and fluid balance during recreational exercise in physically active adults.

METHODS: Fifty-two physically active adult male (n = 31) and female (n = 21) subjects aged 36 ± 12 years (mean ± SD); body mass 80.7 ± 15.9 kg; volunteered to participate at a fitness centre. Urine samples were collected upon arrival. Nude body mass was recorded before and after exercise. Subjects performed a freely chosen gymnasium-based exercise session in mean ambient conditions of 21 oC and 55% relative humidity, with ad libitum access to water. Sweat loss was estimated from the change in body mass after correction for fluid intake and urinary losses.

RESULTS: Mean ± SD (range) exercise duration was 64 ± 22 mins (15 - 125 mins). Pre-exercise urine osmolality was 698 ± 288 mOsmol.kg-1 (166 - 1245 mOsmol.kg-1) and was not different for gender (p = 0.915). Urine osmolality was above 900 mOsmol. kg-1 (used as a threshold for dehydration) in 38% of participants; 32% of males and 43% of females. The change in body mass during exercise was −0.51 ± 0.32 kg (−1.30 - 0.25 kg) and was greater in males than females (−0.59 ±0.35 vs. −0.39 ± 0.23 kg; p< 0.05). This was equivalent to a percentage change in pre-exercise body mass of-0.62 ± 0.2% (−1.63 - 0.40%) which was not different for gender (p = 0.258). Sweat loss was 794 ± 391 ml (50 - 1656 ml) and was greater in males than females (938 ± 390 vs. 556 ± 264 ml; p < 0.01), whilst fluid intake was 390 ± 298 ml (0 - 1610 ml) and was also greater in males than females (468 ± 329 vs. 275 ± 200 ml; p < 0.05).

CONCLUSION: Although there was large inter-individual variability, male and female recreational exercisers generally became modestly dehydrated during a typical exercise session, as insufficient fluid was consumed to replace sweat losses. Furthermore, for many adults this was superimposed on existing dehydration because a large proportion of participants arrived to take part in exercise in a dehydrated state.

© 2007 American College of Sports Medicine