Impaired Muscle Phasing Systematically Adapts to Varied Relative 1 Angular Relationships during Locomotion in People Post - Stroke

27 After stroke, hemiparesis will result in impairments to locomotor control. Specifically, 28 muscle coordination deficits, in the form of inappropriately phased muscle activity patterns, 29 occur in both the paretic and non-paretic limbs. These dysfunctional paretic muscle coordination 30 patterns can adapt to somatosensory inputs and also, the sensorimotor state of non-paretic limb 31 can influence paretic limb. However, the relative contribution of interlimb pathways for 32 improving paretic muscle activation patterns in term of phasing remains unknown. In this study, 33 we investigated whether the paretic muscle activity phasing can be influenced by the relative 34 angular spatial relationship of the non-paretic limb by using a split-crank ergometer, where the 35 cranks could be decoupled. Eighteen participants with chronic stroke were asked to pedal 36 bilaterally during each task while surface EMG signals were recorded bilaterally from four lower 37 extremity muscles (vastus medialis, rectus femoris, tibialis anterior, and soleus). During each 38 experiment, the relative angular crank positions were manipulated by increasing or decreasing 39 their difference by randomly ordered increments of 30° over the complete cycle (0º (in phase 40 41 phase pedaling). We found that the paretic and non-paretic muscle phasing in the cycle 42 systematically adapted to varied relative angular relationships and this systematic relationship 43 was well-modeled by a sinusoidal relationship. Also, the paretic uniarticular muscle (vastus 44 medialis) showed larger phase shifts compared with biarticular muscle (rectus femoris). More 45 importantly, for each stroke subject, we demonstrated an exclusive crank angular relation that 46 resulted in the generation of more appropriately phased paretic muscle activity. These findings 47 provide new evidence to better understanding of the capability of impaired nervous system to 48 produce a more normalized muscle phasing pattern post-stroke.