Motor Characteristics of Human Adaptations to External Assistive Forces.

Technology advancement has enabled the develop-ment of robotic exoskeletons that are portable, pow-erful, and sufficiently smart to be of practical use in the real world. These devices provide partial assis-tive forces that increase their user's physical strength to better meet the demands of everyday life and have potential applications in various settings. Examples include helping older adults maintain their indepen-dence and preventing musculoskeletal injuries among factory workers. Although great strides have been made to improve the performance and usability of these devices, human characteristics and the way hu-mans adapt to the external assistive forces from these devices are rarely explicitly considered in their devel-opment. A common assumption is that if the provided assistive forces are aligned with the intent of users, users can easily "switch off" their muscles and effec-tively utilize this assistive force. In this review, we demonstrate that human adaptations to external as-sistive forces can lead to inefficiencies or conflicts that decrease the effectiveness of robotic exoskeletons. We then discuss the motor characteristics of human adap-tations to external assistive forces.