Pairing limb posture feedback with an ankle exoskeleton to augment limb propulsion.

Area of Science:

• Biomechanics
• Human Movement Science
• Rehabilitation Engineering

Background:

• Limb propulsion deficits are common in clinical populations, often due to reduced plantarflexor moment or trailing limb angle (TLA).
• Ankle exoskeletons (EXOs) can increase plantarflexor moment, but a concurrent decrease in TLA has limited their effectiveness in improving propulsion, particularly in post-stroke individuals.
• Understanding the interplay between TLA and EXO assistance is crucial for optimizing gait rehabilitation strategies.

Purpose of the Study:

• To investigate the combined effects of ankle exoskeleton (plantarflexor) assistance and TLA feedback on gait propulsion.
• To analyze the impact on joint mechanics and margins of stability during walking.
• To determine if TLA feedback can mitigate the negative effects of reduced TLA often seen with EXO use.

Main Methods:

• Ten unimpaired individuals walked on an instrumented treadmill with an ankle exoskeleton.
• Participants received visual feedback to modulate their peak TLA to baseline-5°, baseline, or baseline+5°.
• EXO plantarflexor torque was applied at 0%, 15%, and 35% bodyweight assistance levels.

Main Results:

• Propulsive impulse significantly increased with higher TLA, independent of EXO assistance.
• Higher EXO assistance shifted mechanical work proximally, increasing the ankle's contribution to total ankle and hip work.
• Increased TLA reduced anteroposterior margin of stability, while higher EXO assistance increased it.

Conclusions:

• Gait propulsion can be enhanced by increasing TLA through feedback, but this may compromise stability.
• Ankle exoskeletons alone did not improve propulsion; however, combining them with TLA feedback shows potential.
• Visual feedback to maintain TLA while using ankle EXOs may enable the conversion of joint benefits into improved limb propulsion for individuals with plantarflexor deficits.