ESMAC Best Paper 2024: Defining exoskeleton aim matters: Simulating optimal assistive moments with explicit...

Area of Science:

• Biomechanics
• Robotics
• Human-Computer Interaction

Background:

• Musculoskeletal simulations inform strategies for motion assistance and muscle dynamics.
• Exoskeletons can supplement muscle forces for various objectives like reduced effort or distributed load.

Purpose of the Study:

• To present a simulation framework for identifying optimal assistance strategies.
• To formulate optimal assistance as a bilevel optimization problem within an inverse simulation scheme.

Main Methods:

• Employed a bilevel optimization approach for assistive moment calculation.
• Solved muscle redundancy problems iteratively to find optimal assistive moments.
• Predicted optimal assistance for ankle and hip movements across three aims: minimal muscle activations, metabolic rates, and moments.

Main Results:

• Optimal assistive moment trajectories are unique and dependent on the specific assistive aim.
• Differences in assistance are explained by muscle-level force contributions and mechanical work.
• Minimal metabolic rate assistance predicted timing and duration consistent with experimental findings.

Conclusions:

• Explicit formulation of the assistive aim is crucial for studying human-device interaction.
• The simulation framework provides a systematic method for determining optimal assistance.