Motoyama, K.; Tashiro, T.; Saito, A.; Horiuchi, M.; Sakaki, T.; Abe, D.

Background: The 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. Research question: How are anteroposterior and lateral gait variabilities influenced by sinusoidal speed changes with different amplitudes ({+/-}0.33 vs. {+/-}0.67 m/s) and periods (30 vs. 60 s)? Which limbs are responsible for the step variabilities in these conditions? Methods: We quantified the IC plane thickness, coefficient of variance of step width (CVSW), time delay of step length (TDSL), and step frequency (TDSF) in 18 healthy young adults. We applied statistical parametric mapping for the time courses of each limb angle during the acceleration and deceleration phases. Results: The IC plane thickness was greater in the {+/-}0.67 m/s condition than in the {+/-}0.33 m/s 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. Significance: Sinusoidal 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.