Segmental mechanical energy changes during sit-to-stand in early subacute stroke under paretic knee constraint

Early mobilization after stroke is associated with better recovery; however, the biomechanics of sit-to-stand in the early subacute phase remain insufficiently understood. Sit-to-stand is a prerequisite for subsequent upright mobility; thus, characterizing sagittal-plane segmental movement patterns during this task may provide information relevant to early rehabilitation assessment. Sixteen patients with subacute stroke (mean 18 days post-onset) and 16 elderly controls performed sit-to-stand. Patients underwent testing under normal and knee-constrained conditions. Wireless inertial measurement units and surface electromyography were used to quantify segmental mechanical energy change, trunk kinematics, and muscle activity. Compared with elderly controls, patients with early subacute stroke showed greater pre-seat-off thorax segmental mechanical energy change. In the stroke group, paretic knee constraint reduced pre-seat-off thorax segmental mechanical energy change compared with the normal condition. Kinematic angle outcomes did not show correction-robust within-stroke condition effects, and exploratory EMG findings were treated as supplementary observations rather than confirmatory evidence for the primary biomechanical interpretation. Task-performance descriptors, including movement duration and rising speed, did not differ significantly between the normal and knee-constrained conditions. These findings suggest that paretic knee constraint modifies sagittal-plane segmental movement organization during sit-to-stand without evidence of gross slowing of task execution. Therefore, segmental mechanical energy analysis may help characterize sagittal-plane segmental movement organization during early post-stroke rehabilitation.