Li L, Tong KY, Hu X. The effect of poststroke impairments on brachialis muscle architecture as measured by ultrasound. Objective: To evaluate the joint angle dependence of brachialis muscle architecture at rest and changes in brachialis muscle architecture during isometric voluntary contractions in people after stroke. Design: The pennation angle and fascicle length of the brachialis muscle were measured in the affected and unaffected sides of people after stroke at 9 different elbow angles ranging from 10° to 90° at the rest condition. Measurements were also carried out at a fixed joint angle of 90° while the subjects were performing isometric muscle contractions at 5 incremental levels of maximal voluntary contraction (MVC) from 20% to 100% of MVC. The data obtained from the affected and unaffected sides of the subjects were compared. Setting: A research laboratory in a rehabilitation center. Participants: Seven hemiplegic adults after stroke with passive range of motion in the elbow from 10° to 90° and Modified Ashworth Scale score larger than 1 were recruited. Interventions: Not applicable. Main Outcome Measures: Ultrasonography was used to measure brachialis muscle pennation angle and fascicle length at the rest condition and during isometric contractions. Results: The measured pennation angles and fascicle lengths were found to be joint-angle-dependent in both the affected and unaffected groups at the rest condition. Further comparisons found that the pennation angles of the affected brachialis muscle were significantly larger (P20°). As the level of isometric voluntary contraction was increased incrementally from 20% to 100% of MVC, the results showed that pennation angle increased significantly (P