Gender differences in ground reaction force following perturbations in subjects with low back pain.

The purpose of this cross-sectional study was to investigate whether gender differences exist in postural reaction when examining response time and amplitude of normalized ground reaction force (GRF) in subjects with low back pain (LBP). Alterations in GRF following sudden perturbations have led to an increased awareness of the postural compensatory mechanism. Although no specific perturbations have been shown to elicit gender differences, GRF can indirectly measure body sway increases more in subjects with LBP. Eighteen male and eighteen female subjects with LBP participated in this study. Subjects were exposed to sudden perturbations (unexpected and expected) by dropping a weighted ball onto a hand-held pan while subjects stood on the force plate. The amplitude of the normalized GRF and response time were calculated from the instance of perturbation to the first peak of the GRF response measured at the force plate. For the female subjects, the amplitude of the normalized GRF significantly decreased during expected perturbations (F(1,33)=4.23, p<0.04). However, the amplitude for the male subjects did not change during either type of perturbation. The response time was not significantly different between genders (F(1,33)=0.25, p=0.61). The male subjects were better able to stabilize their postural stability after an unexpected perturbation, which reveals postural integrity of compensatory mechanisms. These results indicated that gender differences exist when examining the amplitude of the normalized GRF following sudden perturbations for subjects with LBP.