Speed amplitude and period affect gait variability and step followability under sinusoidal speed changing conditions

BackgroundThe time courses of the joint elevation angles of the thigh, shank, and foot in one stride during walking can be well approximated by a "plane" in a triaxial space. This intersegmental coordination (IC) of the lower limb elevation angles is called planar covariation law. Thickness of the IC plane is associated with gait variability. This study aimed to examine how anteroposterior and lateral gait variabilities are influenced by sinusoidal speed changes with different amplitudes ({+/-}0.33 vs. {+/-}0.67 m{middle dot}s-1) and periods (30 vs. 60 s). We also questioned which limbs are responsible for the step variabilities in these conditions. MethodsEighteen young adults walked on a treadmill under sinusoidal speed-changing conditions with different amplitudes ({+/-}0.33 vs. {+/-}0.67 m{middle dot}s-1) and periods (30-vs. 60-s). Using 3D motion analysis system, we quantified the IC plane thickness, coefficient of variance of step width (CVSW), time delay of step length (TDSL), and step frequency (TDSF). We applied 2-way statistical parametric mapping for the time courses of each limb angle during the acceleration and deceleration phases. ResultsThe IC plane thickness was greater in the {+/-}0.67 m{middle dot}s-1 condition than in the {+/-}0.33 m{middle dot}s-1 condition. Periods and amplitudes did not affect CVSW, TDSL, and TDSF. In the middle gait cycle, the thigh and shank were delayed in the greater amplitude condition during the acceleration phase but proceeded in the same condition during the deceleration phase. DiscussionSinusoidal speed amplitude influenced anteroposterior gait variability, but not lateral gait variability, regardless of period, even in healthy young adults. More distal limbs were delayed in the greater speed amplitude condition during the acceleration phase, whereas more proximal limbs proceeded in that condition during the deceleration phase, indicating that these different behaviors of the lower limb segments could be related to step variabilities.