Effects of inclined surfaces on gait variability and stability in unilateral lower limb amputees

This study aims to analyze gait variability and stability of individuals with amputation walking on upward (8%), horizontal (0%), and downward (- 8%) inclines, by using linear and nonlinear descriptors. Trunk linear variability and gait spatiotemporal parameters were evaluated. Nonlinear variability (local dynamic stability-LDS), was estimated by the maximum Lyapunov exponent (λ) computed from a trunk marker velocity. The gait descriptors were compared among three distinct groups (N participants): unilateral transtibial amputees (TTA, N = 12); unilateral transfemoral amputees (TFA, N = 13); control group (CT, N = 15). For step width and support phase, the effect of inclination was greater for TFA group, especially in the DOWN condition. Linear variability was higher for amputees (TFA and TTA) especially in the UP condition in the medial-lateral and anterior-posterior directions. TTA and TFA groups presented greater λ values than CT group in medial-lateral direction indicating decreased LDS, but TFA group presented smaller λ values than TTA and CT groups in the V direction. Our findings showed that inclination introduced significant changes in the estimated parameters for all groups, with greater changes for amputee groups. Furthermore, the level of amputation directly affects the analyzed gait parameters being the TFA group the one which presents greater changes. Graphical abstract The objective of this study was to analyze gait variability of individuals with amputation walking on (A) upward (+ 8%), (B) horizontal (0%), and (C) downward (- 8%) inclines, by using linear and nonlinear biomechanical descriptors. Linear measures of variability, such trunk variability and gait spatiotemporal parameters were evaluated. Nonlinear variability was estimated by the exponent of divergence (maximum Lyapunov exponent) of the velocity of a marker fixed in the subject's trunk while walking on inclined surfaces.