Tapping into skeletal muscle biomechanics for design and control of lower-limb exoskeletons: a narrative review

Lower-limb exoskeletons and exosuits (“exos”) are traditionally designed with a strong focus on mechatronics and actuation, whereas the “human-side” is often disregarded or minimally modelled. Muscle biomechanics principles and skeletal muscle response to robot-delivered loads should be incorporated in design/control of exos. In this narrative review, we summarize the advances in literature with respect to the fusion of muscle biomechanics and lower-limb exoskeletons. We reported methods to measure muscle biomechanics directly and indirectly and summarized the studies that incorporated muscle measures for improved design and control of intuitive lower-limb exos. Finally, we delved into articles that studied how the human-exo interaction influenced muscle biomechanics during locomotion. To support neurorehabilitation and facilitate everyday use of wearable assistive technologies, we believe that future studies should investigate and predict how exoskeleton assistance strategies would structurally remodel skeletal muscle over time. Real-time mapping of the neuromechanical origin and generation of muscle force resulting in joint torques should be combined with musculoskeletal models to address time varying parameters such as adaptation to exos and fatigue. Development of smarter predictive controllers that steer rather than assist biological components could result in a synchronized human-machine system that optimizes the biological and electromechanical performance of the combined system