Closing the loop between wearable technology and human biology: a new paradigm for steering neuromuscular form and function

Wearable technologies such as bionic limbs, robotic exoskeletons and neuromodulation devices have long been designed with the goal of enhancing human movement. However, current technologies have shown only modest results in healthy individuals and limited clinical impact. A central element hampering progress is that wearable technologies do not interact directly with tissues in the composite neuromuscular system. That is, current wearable systems do not take into account how biological targets (e.g. joints, tendons, muscles, nerves) react to mechanical or electrical stimuli, especially at extreme ends of the spatiotemporal scale (e.g. cell growth over months or years). Here, we outline a framework for ‘closing-the-loop’ between wearable technology and human biology. We envision a new class of wearable systems that will be classified as ‘steering devices’ rather than ‘assistive devices’ and outline the suggested research roadmap for the next 10–15 years. Wearable systems that steer, rather than assist, should be capable of delivering coordinated electro-mechanical stimuli to alter, in a controlled way, neuromuscular tissue form and function over time scales ranging from seconds (e.g. a movement cycle) to months (e.g. recovery stage following neuromuscular injuries) and beyond (e.g. across ageing stages). With an emphasis on spinal cord electrical stimulation and exosuits for the lower extremity, we explore developments in three key directions: (a) recording neuromuscular cellular activity from the intact moving human in vivo, (b) predicting tissue function and adaptation in response to electro-mechanical stimuli over time and (c) controlling tissue form and function with enough certainty to induce targeted, positive changes in the future. We discuss how this framework could restore, maintain or augment human movement and set the course for a new era in the development of bioprotective wearable devices. That is, devices designed to directly respond to biological cues to maintain integrity of underlying physiological systems over the lifespan.