Nonlinear dose-response relationships between psychological and behavioral factors and training quality among firefighters: a restricted cubic spline analysis

Background Firefighters are exposed to multiple occupational health risks, including physical fatigue, psychological stress, and traumatic events. Although several psychological and behavioral factors have been identified as potential determinants of training quality, most prior studies assumed linear associations, which may not fully capture the true functional relationships. This study aimed to examine whether nonlinear dose-response relationships exist between six key psychological and behavioral factors and daily training quality among firefighters, and to identify inflection points and threshold effects. Methods A cross-sectional survey was conducted among 1,587 professional firefighters from seven provinces, municipalities, and autonomous regions in China. Restricted cubic spline (RCS) models with four knots were applied to assess both overall and nonlinear associations between each psychological-behavioral variable and training quality, while controlling for the remaining variables and relevant demographic covariates (age, educational attainment, household registration type, and marital status). Results All six psychological and behavioral variables demonstrated significant nonlinear associations with training quality: sleepiness ( F = 15.31, p < 0.001), occupational stress ( F = 11.20, p < 0.001), self-efficacy ( F = 14.42, p < 0.001), emotional exhaustion ( F = 11.38, p < 0.001), social support ( F = 15.83, p < 0.001), and work-family conflict ( F = 6.29, p = 0.002). The complete multivariable model explained 48.6% of the variance in training quality (R 2 = 0.486). Dose-response curves revealed distinct threshold effects and curvature patterns for each variable. Conclusion The associations between most psychological and behavioral factors and firefighter training quality are not simply linear; rather, they exhibit varied inflection and threshold effects. These findings have important theoretical and practical implications for the design of precision psychological intervention strategies.