RESUMEN
BACKGROUND: Firefighting is a physically demanding profession. Firefighters (FFs) need adequate physical fitness (PF) to perform duty tasks efficiently. While FFs' work demands are constant throughout their career, there is an expected age-related decline in PF. OBJECTIVE: To describe longitudinal changes in cardiorespiratory fitness (CRF) based on a fixed (12.0 METs) and an age-adjusted standard and compare the prevalence of fit/unfit firefighters (FFs) over eight years. METHODS: 297 Brazilian male firefighters were randomly selected. CRF was assessed by the 12-minute Cooper test. To compare the prevalence's of fit/unfit FFs depending on the standard (12 METs vs. age-adjusted), the McNemar test was used. RESULTS: The reduction in the prevalence of fit firefighters was 4.4-fold higher when the analysis did not consider age. CONCLUSION: After eight years, the prevalence of fit FFs decreased by 30.5% based on the fixed standard, while this reduction was only 7% when using an age-adjusted standard.