Theoretical discrimination index of postural instability in amyotrophic lateral sclerosis

To assess the usefulness of a theoretical postural instability discrimination index (PI th ) in amyotrophic lateral sclerosis (ALS). Prospective regression analyzes were performed to identify the biomechanical determinants of postural instability unrelated to lower limb motor deficits from gait initiation factors. PI th was constructed using a logit function of biomechanical determinants. Discriminatory performance and performance differences were tested. Backward displacement of the pression center (APA amplitude ) and active vertical braking of the mass center (Braking-index) were the biomechanical determinants of postural instability. PI th = − 0.13 × APA amplitude − 0.12 × Braking-index + 5.67, ( P < 0.0001, RSquare = 0.6119). OR (APA amplitude ) and OR (Braking-index) were 0.878 and 0.887, respectively, i.e., for a decrease of 10 mm in APA amplitude or 10