Tear osmolarity is sensitive to exercise-induced fluid loss but is not associated with common hydration measures in a field setting.

This investigation (i) examined changes in tear osmolarity in response to fluid loss that occurs with exercise in a field setting, and (ii) compared tear osmolarity with common field and laboratory hydration measures.  Sixty-three participants [age 27.8 ± 8.4 years, body mass 72.15 ± 10.61 kg] completed a self-paced 10 km run outside on a predetermined course. Body mass, tear fluid, venous blood and urine samples were collected immediately before and after exercise.  Significant (p < 0.001) reductions in body mass (1.71 ± 0.44%) and increases in tear osmolarity (8 ± 15 mOsm.L-1 ), plasma osmolality (7 ± 8 mOsm.kg-1 ), and urine specific gravity (0.0014 ± 0.0042 g.mL-1 ; p = 0.008) were observed following exercise. Pre- to post-exercise change in tear osmolarity was not significantly correlated (all p > 0.05) with plasma osmolality (rs  = 0.24), urine osmolality (rs  = 0.14), urine specific gravity (rs  = 0.13) or relative body mass loss (r = 0.20).  Tear osmolarity is responsive to exercise-induced fluid loss but does not correlate with the changes observed using other common measures of hydration status in the field setting. Practitioners shouldn't directly compare or replace other common hydration measures with tear osmolarity in the field.

ABBREVIATIONS: BML: Body Mass Loss; CV: Coefficient of Variation; Posm : Plasma osmolality; SD: Standard Deviation; Tosm : Tear Osmolarity; Uosm : Urine Osmolality; USG: Urine Specific Gravity; WBGT: Wet bulb globe thermometer.