Low-force human-human hand interactions induce gait changes through sensorimotor engagement instead of direct mechanical effects

Physical human-robot interactions (pHRI) often provide mechanical force and power to aid and alter human walking without requiring voluntary effort from the human. Alternatively, we propose that principles of physical human-human interactions (pHHI) can inspire pHRI that aids walking by engaging human sensorimotor processes. We hypothesize that low-force hand interactions can intuitively induce people to alter their own walking. Our experiment paradigm is based on partner dancing: an expert partner dancer influences novice participants to alter step frequency solely through hand interactions. Without prior instruction or training, novices decreased step frequency by 29% and increased step frequency 18% based on low forces (< 20 N) at the hands. Power transfer at the hands was 10-100x smaller than that exerted by the lower limbs to propel locomotion, suggesting that the expert did not mechanically alter the novice’s gait. Instead, the direction of hand forces and power may communicate information about desired walking patterns. Finally, the expert altered arm stiffness to match that of the novice, offering a design principle for pHRI to alter gait. Our results provide a framework for developing pHRI with wide-ranging applications, including assistive technology and physical rehabilitation, human-robot manufacturing, physical education, and recreation.