Abstract
Research shows a blend of bilateral influence and independence between leading and trailing limbs during obstacle avoidance. Recent research also shows time constraints in switching leading limb strategies. The present study aimed to understand the ability to switch anticipatory locomotor adjustments (ALAs) in the trailing limb. Ten healthy young adults (24 ± 3 years) were immersed in a virtual environment requiring them to plan and step over an obstacle that, for the trailing limb, could change to a platform, requiring a switch in locomotor strategies to become a leading limb to step onto a new surface. Such perturbations were provoked at either late planning or early execution of the initial trailing limb obstacle avoidance. Sagittal plane trailing limb kinematics, joint kinetics and energetics were measured along with electromyographic activity of key lower limb muscles. Repeated measures ANOVAs compared dependent variables across conditions. To adjust to the new environment, knee flexor power around toe-off decreased (p < 0.001) and hip flexor power increased (p < 0.001) for late planning phase perturbations, while there was only an increase in mid-swing hip flexor power (p < 0.05) during perturbations at execution. Findings showed no influence of the leading limb function on the ability to switch trailing limb ALAs during late planning. However, the trailing limb was also constrained for modifying ALAs once execution began, but on-going limb control strategies could be exploited in a reactive mode.
Highlights
Navigating complex daily environments involves anticipatory control to safely avoid obstacles.There are robust and different lower limb strategies for stepping over an obstacle compared to stepping onto a platform
It appears that all participants tolerated the virtual environment (VE) well given average low group scores of 0.31/3 ± 0.19 on the Simulator Sickness Questionnaire
Average group scores of 5.51/7 ± 0.77 were found on the Presence Questionnaire, and they were 4.54/7 ± 0.68 on the SUS Questionnaire, showing that participants were relatively well immersed
Summary
Navigating complex daily environments involves anticipatory control to safely avoid obstacles. There are robust and different lower limb strategies for stepping over an obstacle compared to stepping onto a platform. The anticipatory locomotor adjustment (ALA) to step over an obstacle involves a knee flexor generation strategy around toe-off (K5) [1,2] for both the leading and trailing limbs (respectively the first and second limbs to adapt) that puts energy in the lower limb to increase both knee and hip flexion. Hip flexor generation power around toe-off (referred to as H3) for limb advancement can be delayed until mid-swing (referred to as H3D) [3,4].
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