title: Non-invasive estimation of hydration status changes through tear fluid osmolarity during exercise and post-exercise rehydration.
abstract: OBJECTIVE
  To determine if tear fluid osmolarity (Tosm) can track changes in hydration status during exercise and post-exercise rehydration.
  
  
  METHODS
  Nineteen male athletes (18-37 years, 74.6 ± 7.9 kg) completed two randomized, counterbalanced trials; cycling (~95 min) with water intake to replace fluid losses or water restriction to progressively dehydrate to 3 % body mass loss (BML). After exercise, subjects drank water to maintain body mass (water intake trials) or progressively rehydrate to pre-exercise body mass (water restriction trials) over a 90-min recovery period. Plasma osmolality (Posm) and Tosm measurements (mean of right and left eyes) were taken pre-exercise, during rest periods between exercise bouts corresponding to 1, 2, and 3 % BML, and rehydration at 2, 1, and 0 % BML.
  
  
  RESULTS
  During exercise mean (± SD) Tosm was significantly higher in water restriction vs. water intake trials at 1 % BML (299 ± 9 vs. 293 ± 9 mmol/L), 2 % BML (301 ± 9 vs. 294 ± 9 mmol/L), and 3 % BML (302 ± 9 vs. 292 ± 8 mmol/L). Mean Tosm progressively decreased during post-exercise rehydration and was not different between trials at 1 % BML (291 ± 8 vs. 290 ± 7 mmol/L) and 0 % BML (288 ± 7 vs. 289 ± 8 mmol/L). Mean Tosm tracked changes in hydration status similar to that of mean Posm; however, the individual responses in Tosm to water restriction and water intake was considerably more variable than that of Posm.
  
  
  CONCLUSIONS
  Tosm is a valid indicator of changes in hydration status when looking at the group mean; however, large differences among subjects in the Tosm response to hydration changes limit its validity for individual recommendations.
authors.affiliation: Gatorade Sports Science Institute, 617 W. Main St., Barrington, IL, 60010, USA, corey.ungaro1@pepsico.com.
authors.forename: Corey T
authors.initials: CT
authors.lastname: Ungaro
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Reimel
authors.forename: Ryan P
authors.initials: RP
authors.lastname: Nuccio
authors.forename: Kelly A
authors.initials: KA
authors.lastname: Barnes
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Pahnke
authors.forename: Lindsay B
authors.initials: LB
authors.lastname: Baker
mesh_terms: D000293:Adolescent; D000328:Adult; D003681:Dehydration / Q000503:physiopathology / Q000628:therapy*; D004326:Drinking / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005440:Fluid Therapy; D006801:Humans; D008297:Male; D014882:Water-Electrolyte Balance / Q000502:physiology*; D055815:Young Adult