Coordination dynamics and speed-related adaptations in forward and backward walking.

This study investigated the effects of walking speed and direction on gait coordination dynamics in healthy young adults, focusing on intralimb and interlimb coordination during forward (FW) and backward (BW) walking. Twenty participants walked on a treadmill under six speed conditions in both FW and BW. Kinematic data were collected to compute spatiotemporal gait parameters, continuous relative phase (CRP), and phase coordination index (PCI) as measures of segmental coordination and bilateral timing. Repeated-measures ANOVAs were used to assess the effects of speed independently for each walking direction. In FW, increased walking speed was associated with longer step and stride lengths, reduced double-limb support time, and lower PCI values. Speed-related changes in CRP were swing and stance phase-specific, with more temporally consistent segmental phase relationships at higher speeds. In BW, slower speeds were associated with higher PCI values and greater phase variability, whereas increases in speed were accompanied by modest, phase-specific changes in CRP. Proximal segment couplings (thigh–shank and thigh–pelvis) were especially sensitive to speed manipulation in both walking directions. Overall, walking speed acted as a control parameter that reorganized intralimb and interlimb coordination in a phase-specific manner. These findings highlight the importance of considering both speed and direction when evaluating gait coordination and provide a coordination-dynamics–based framework for future investigations in clinical populations with impaired locomotor control.