Comparing Metabolic Cost and Muscle Activation for Knee and Back Exoskeletons in Lifting

Performing heavy manual lifting jobs can be extremely strenuous, often resulting in high rates of injury at overloaded joints. Lower-body exoskeletons have potential to mitigate this fatigue and injury through targeted joint assistance. A variety of current wearable devices aim to provide this kind of support, but their effects on both directly and indirectly targeted joints have not been fully investigated. In this study, a powered bilateral knee exoskeleton (research device), and passive back exosuit (HeroWear Apex) were compared across 10 individuals through a battery of manual lifting tasks. Metabolic, electromyographic, and subject-reported outcome measure data were used to determine which exoskeleton provided the best assistance for each task type. It was found that the knee exoskeleton significantly reduced metabolic cost by$\mathbf {9.6\%}$compared to the no-exoskeleton baseline$(\mathbf {p < .05})$. Both the knee and back exoskeletons reduced activation in up to 6 of the muscles measured (out of 16). Importantly, each device primarily reduced muscle activation around the joint it targeted, not around adjacent joints. These findings suggest that exoskeletons that target the knee or lower back joint during lifting can provide significant assistance in reducing exertion.