Muscle strength of males and females with chronic primary low back pain is associated with gait parameters: a cross-sectional study of the BACKFIT project.

Introduction Individuals with chronic primary low back pain (CPLBP) present muscular deconditioning that triggers difficulties while walking. The aim was to explore the associations between muscle strength and spatiotemporal gait parameters in people with CPLBP. Design Cross-sectional study. Setting Clinical setting. Participants 104 (68 females) individuals with CPLBP. Main outcome measures Back flexors and extensors, and lower- and upper-body muscle strength were measured with field-based fitness tests (prone bridging, Biering-Sørensen, 30-second chair stand test and TKK 5101 hand grip dynamometer, respectively). Overall muscle strength was derived from each fitness test using z-score standardization. Spatiotemporal gait parameters were measured with the Optogait™ platform. The mean value and coefficient of variation of each variable were calculated. Results Linear regression analysis showed that, in females, greater overall muscle strength was associated with shorter contact time (95% confidence interval for B=-0.09, -0.03), stride cycle-time (-0.09, -0.02) and double support (-0.08, -0.03), lower load response (-0.04, -0.02), higher gait speed (0.11, 0.27) and longer stride length (7.3, 18.4) (all, p <0.004). In males, greater overall muscle strength was associated with shorter double support (-0.08, -0.003), lower load response (-0.04, -0.001), higher gait speed (0.03, 0.26) and longer stride length (1.9, 16.3) (all, p <0.037). Conclusions Greater overall muscle strength was consistently associated with better performance in all spatiotemporal gait parameters in individuals with CPLBP. Notably, our results reveal sex-specific associations: back extensor strength is the primary predictor of gait performance in males, while back flexor strength emerged as the dominant in females. These findings suggest that CPLBP-related muscular impairments differ between sexes, which highlights the need for tailored clinical interventions.