Urinary indices during dehydration, exercise, and rehydration

Int J Sport Nutr. 1998 Dec;8(4):345-55. doi: 10.1123/ijsn.8.4.345.


This investigation evaluated the validity and sensitivity of urine color (Ucol), specific gravity (Usg), and osmolality (Uosm) as indices of hydration status, by comparing them to changes in body water. Nine highly trained males underwent a 42-hr protocol involving dehydration to 3.7% of body mass (Day 1, -2.64 kg), cycling to exhaustion (Day 2, -5.2% of body mass, -3.68 kg), and oral rehydration for 21 hr. The ranges of mean (across time) blood and urine values were Ucol, 1-7; Usg, 1.004-1.029; Uosm, 117-1,081 mOsm x kg-1; and plasma osmolality (Posm), 280-298 mOsm x kg-1. Urine color tracked changes in body water as effectively as (or better than) Uosm, Usg, urine volume, Posm, plasma sodium, and plasma total protein. We concluded that (a) Ucol, Uosm, and Usg are valid indices of hydration status, and (b) marked dehydration, exercise, and rehydration had little effect on the validity and sensitivity of these indices.

Publication types

  • Clinical Trial
  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Body Fluids*
  • Body Mass Index
  • Dehydration / blood
  • Dehydration / urine*
  • Fluid Therapy*
  • Humans
  • Male
  • Osmolar Concentration
  • Physical Exertion / physiology*
  • Sensitivity and Specificity
  • Sodium / blood
  • Specific Gravity
  • Sports Medicine
  • Water-Electrolyte Balance


  • Sodium