Do speed amplitude and period affect gait variability and step followability under sinusoidal speed changing...

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 associated with gait variability. This study aimed to examine how anteroposterior and lateral gait variabilities are influenced by different amplitudes (±0.33 vs. ± 0.67 m·s^-1) and periods (30 vs. 60 s) of sinusoidal speed changes. We also examined which limbs are responsible for the step variabilities.

The IC plane thickness and coefficient of variance of step width (CV_SW) were quantified as anteroposterior and lateral gait variability in 18 young adults. Time delay of step length (TD_SL) and step frequency (TD_SF) against sinusoidal speed changes were determined. Two-way statistical parametric mapping was applied for the time courses of each limb angle.

The IC plane thickness was greater in the ±0.67 m·s^-1 condition than the ±0.33 m·s^-1 condition. Neither periods nor amplitudes affected CV_SW, TD_SL, and TD_SF. In the middle gait cycle, shank and foot angles were delayed against sinusoidal speed changes in the ±0.67 m·s^-1 condition during acceleration phase, whereas shank and thigh angles proceeded in that condition during deceleration phase.

Amplitude of sinusoidal speed changes increased anteroposterior, but not lateral, gait variability regardless of period. Distal and proximal limbs are controlled differently when continuous step adjustments are required, and this may be attributed to step variabilities.