Firefighter Years: Mediating Effects of Years of Service on Physical Fitness Original Research

Main Article Content

Joel Martin
Mike Toczko
Angela Miller
Shane Caswell

Keywords

occupational performance, health, emergency responders

Abstract

Introduction: Firefighters' biological age and years of service (YOS) often vary significantly, as individuals may enter the profession at any age. YOS introduces cumulative occupational stressors that may mediate age-related declines in physical fitness. While age-related reductions in physical fitness are well-documented, the mediating effect of YOS on firefighters' fitness remains unclear. Thus, the purpose of this study was to investigate the mediating role of YOS in the relationship between age and physical fitness outcomes and assess whether sex moderates the effects of YOS on these outcomes.


Methods:  A retrospective analysis of physical fitness testing data from 2019 to 2021 of 1,281 firefighters (1,136 males, 145 females; Age: 39.2 ± 9.3 years; YOS: 11.0 ± 7.3 years) was conducted. Fitness tests included maximum pull-ups (PL), push-ups within 60 seconds (PU), sit-ups within 60 seconds (SU), and a 3-minute step test to estimate VO2max. Pearson’s correlation tested the relationship between age and YOS, while path analysis evaluated YOS as a mediator between age and fitness outcomes. A moderation analysis examined the influence of sex on these relationships.


Results: Age and YOS were moderately correlated (r = 0.66). YOS fully mediated the relationship between age and SU (p < 0.001) and partially mediated the effects of age on PL (p < 0.001) and PU (p < 0.001). No mediation effect of YOS was observed for VO2max (p > 0.05). Sex significantly moderated the relationship between age, YOS, and several physical fitness outcomes. Specifically, the relationship between age and pull-up performance was stronger for males (b = -0.152, p < 0.001) than females (b = -0.065, p < 0.05), while YOS was significantly related to pull-up performance in males (b = -0.123, p < 0.001) but not in females (b = -0.071, p > 0.05).


Conclusions: YOS exacerbates declines in musculoskeletal strength and endurance, independent of age, particularly in male firefighters. Fire departments should consider YOS and sex, alongside age, when designing fitness assessments and training programs to optimize performance and safety.

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