Adaptation process for standing postural control in individuals with hemiparesis.

PURPOSE: To study the adaptation process for standing postural control in patients with hemiparesis after stroke. METHODS: The changes of a standing posture developed in nine hemiparetic patients who had never maintained an upright stance alone (aged 48-62 years; 6-19 days after stroke) was evaluated by recording ground reaction forces and surface electromyographic (EMG) from lower limbs. A 60-s standing trial without any instruction about body alignment was repeated five times, and the experience-related changes of centre of pressure (COP) and integrated EMG data were estimated. RESULTS: In the early standing trials, patients balanced themselves by managing the average COP position around the midline of both feet, accompanied by increased muscular activity of the non-paretic leg. COP displacement gradually decreased in the later standing trials (P < 0.05). Postural adaptations were achieved by shifting the centre of body sway to the side of the non-paretic foot (P < 0.05) while reducing biceps femoris muscular activity (P < 0.01) in the non-paretic leg. CONCLUSIONS: This study revealed that weight-bearing asymmetry might contribute to improving increased body sway and muscular over-activity of the non-paretic leg. When planning rehabilitative treatment for hemiparetic patients, we should consider that weight-bearing asymmetry may be a result of systematic postural control.