The current progress of active compliance control strategies and applications in lower limb exoskeleton rehabilitation robot: a narrative review.

INTRODUCTION: With the increasing requirements for performance and safety of lower limb exoskeleton rehabilitation robots, researchers are exploring various active compliance control strategies to improve the compliance of control and enhance safety and effectiveness of the rehabilitation training. The focus of this paper is to evaluate existing active compliance control strategies applied to lower limb exoskeleton rehabilitation robots, highlighting their principles, key technologies and performance. AREAS COVERED: Literature searches were conducted in PubMed and Web of Science from 2000 to 2025, starting with the broad keyword 'active compliance control strategy' and narrowing down to specific aspects such as 'impedance control.' 69 articles were reviewed and 8 active compliance control strategies were divided into 3 categories according to their core principles: impedance control (n = 18), force and position hybrid control (n = 27) and machine learning-based hybrid control (n = 24). Their applications in 5 types of lower limb exoskeleton rehabilitation robots are outlined. EXPERT OPINION: Active compliance control strategies for lower limb exoskeleton rehabilitation robots are necessary for safe human-robot interaction and assist-as-needed implementation. This paper envisions a concept of an active compliance controller that covers the entire rehabilitation cycle, ensuring that the robot is continuously aligned with the patient's rehabilitation needs.