Assistance level versus metabolic cost in a biarticular exoskeleton: a simulation study

Exoskeletons can augment the capacity of humans and enhance mobility in the disabled. Often it is required to understand how varied levels of assistance affect the metabolic cost. Experimental studies investigated the effect of varied assistance on metabolic cost for different exoskeletons . Simulations can complement experiments.Here we investigate how different levels of assistance affect metabolic cost in loaded walking with a biarticular knee-ankle exoskeleton and compare it with monoarticular ankle exoskeleton. Exoskeleton was modeled as ideal actuator. We used computed muscle control algorithm in OpenSim to estimate muscle and actuator controls to track the experimental data. Different levels of assistance was considered by varying the maximum force that the actuator can produce. Metabolic cost was computed using Umberger's metabolics model. The results provide a reference for deciding the amount of assistance required based on design and biomechanical constraints and optimal torque profile for ankle and knee-ankle exoskeletons.