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Two crucial, multi-articular strategies for anticipatory locomotor adjustments (ALA) are knee flexor generation to step over obstacles and hip flexor generation to step up. While lower limb control can be adapted online to modify an already planned obstacle avoidance, or to avoid the sudden appearance of an obstacle, it is not known whether a planned ALA can be substituted by different one online. The present objective was to study such ALA substitutions at two specific timepoints: the final planning stage and the initiation of ALA execution. Ten healthy, young adults (22.0 ± 1.7 years; 5 males) walked in a Virtual Environment (VE) representing the laboratory within a head mounted display. Two blocks of trials, one involving an initial VE with an obstacle (OB) and the other an initial VE with a platform (PL) (heights of 15% of lower limb length for both), were presented, where the initial VE could remain unchanged or be randomly switched between them at one of the two timepoints. The final VE always corresponded to the real environment. Lead limb kinematics, joint kinetics and energetics, as well as electromyography were measured. Repeated measures ANOVAs were used to compare across conditions. Foot clearance, knee flexor generation, and hip flexor generation all changed in the expected directions for the final VEs when requiring early substitution, but not when switched late. These findings show that volitional, locomotor strategies may be substituted at the end of the ALA planning phase, but not once execution is initiated.

Many individuals, such as persons with spinal cord injury (SCI), rely on wheeled locomotion involving manual (MWC) or power (PWC) wheelchairs to navigate their environments. Yet, visuo-locomotor control underlying WC navigation in experienced users is not well understood. The objective of this study was to compare the visuo-locomotor control between MWC and PWC in individuals with SCI while changing direction and circumventing an obstacle. Participants with SCI using a MWC (n = 12, 38.5 ± 10.7 years) or a PWC (n = 10, 47.8 ± 8.6 years) were asked to maneuver their chair straight ahead, while changing direction 45° to the right, and while circumventing an obstacle to the right, all at self-selected speeds. Speed, minimal clearance, point of deviation, temporal body and WC coordination, relative timing of segment rotations and visual behavior were analyzed. There was no main effect of group for speed, clearance and point of deviation. During direction change, the head always led body and wheelchair reorientation while an "en bloc" strategy was used for circumventing obstacle for both groups. In straight-ahead locomotion, participants predominantly fixed their gaze on the end target. During direction change and obstacle circumvention, participants fixated more on the future path and the obstacle for both WC modes. Overall, specific gaze behavior depended on environmental demands. While MWC and PWC users adopt similar navigational strategies and visuo-locomotor coordination while changing direction and circumventing obstacle, there were some differences in the amount of head rotation that could be related to a counter-movement used more by PWC users.