Ankle exoskeleton assistance increases task-relevant variability without altering center of mass control during...

Area of Science:

• Biomechanics
• Robotics
• Human Movement Science

Background:

• Ankle exoskeletons modify walking mechanics, but their impact on overall body coordination is not well understood.
• Investigating motor variability and center-of-mass (CoM) movement during exoskeleton-assisted walking is crucial for understanding human-robot interaction.

Purpose of the Study:

• To examine how ankle exoskeleton assistance affects the structure of motor variability during walking.
• To determine the influence of exoskeletons on center-of-mass (CoM) movement and whole-body coordination.

Main Methods:

• Twenty healthy adults walked with and without ankle exoskeleton assistance.
• Whole-body kinematics were recorded, and joint variability was analyzed using the Uncontrolled Manifold (UCM) approach.
• CoM movement was analyzed in three dimensions, with statistical parametric mapping used to assess gait cycle differences.

Main Results:

• Exoskeleton assistance increased joint variability that influences CoM (UCM⊥) but did not alter variability that doesn't affect CoM (UCM||) or the stabilizing synergy ratio (UCMratio).
• No significant differences in mediolateral or anteroposterior CoM movement were observed.
• Small, condition-dependent differences in vertical CoM displacement were noted during specific phases of the gait cycle.

Conclusions:

• Ankle exoskeletons alter joint-level variability but preserve overall CoM control and whole-body coordination in healthy adults.
• Assistive devices should be designed to support walking without compromising balance and CoM control.
• Findings inform the clinical application of exoskeletons, emphasizing the need for seamless integration with human motor control.