I. Introduction
Limb coordination analysis has attracted enough interest for decades due to its medical health care and healthcare assessment [1], [2]. Typically, monitoring real-world lower-limb function in individuals with lower-limb impairments, especially for those undergoing rehabilitation after a neurological event, provides clinically important information [3]. Surface electromyography (sEMG) is a noninvasive recording of muscle activity that gives an indication of limb coordination [4], [5]. During human motion process, the central nervous system transmits limb motion information to neuromuscular control through nerve oscillation [6]. More importantly, intermuscular coupling is also a bridge that could relate limb coordination to neuromuscular control. Specifically, patterns of interlimb coordination and its variability provide insights into neuromuscular control during movement [2]. Hence, the lower-limb coordination between thigh and shank from the nonlinear intermuscular coupling of sEMG has become the key. More precisely, it is beneficial for understanding the functional state of muscles, and then exploring the pathological mechanism of human motion control and motor dysfunction. With the popularity of sEMG wearable sensing equipment, the lower-limb movement analysis by measuring muscle state has attracted much attention owing to its effects on medical health care [7], [8] and healthcare assessment [9], as shown in Fig. 1.
Application of sEMG in rehabilitation.