Hydration Tracking via Saliva Osmolarity in Recruit Firefighters Throughout a 12-Week Fire School

Background: The purpose of this study was to assess hydration status via saliva osmolarity throughout a 12-week Fire School in recruit firefighters. Methods: At the beginning (AM) and end (PM) of the workday for 13 weeks (a 12-week Fire School and an additional transition week), saliva osmolarity was measured, recorded, and relayed to each participant in the sample, which included 23 recruit firefighters. The average weekly osmolarity scores were computed for AM and PM. Separate linear mixed-effects models were used to assess the changes in osmolarity at each time of day over the course of the training. Bonferroni-adjusted post hoc tests were used to identify significant differences between weeks while maintaining test-wise error (α = 0.05). Results: AM was significantly lower in week 12 than in weeks 4 and 6, and lower in week 13 than in weeks 2, 4, 6, and 7 (p ≤ 0.035 for all). PM was significantly lower in week 12 than in weeks 3 and 7, and was lower in week 13 than in weeks 1, 3, and 7 (p ≤ 0.019 for all). Conclusion: This study demonstrated that hydration status via saliva osmolarity improved during the last half of Fire School despite those weeks being more physically and thermally challenging.