Biomechanical analysis of the sit-to-stand motion in elderly persons.

The sit-to-stand motion of ten healthy subjects, 65 to 76 years old, was evaluated using kinematic, force plate, and electromyographic data to characterize the sit-to-stand motion. Kinematic data collected by video, muscle activity monitored by surface electromyography, and ground reaction forces analyzed by a piezoelectric force plate were used for analysis. Using these synchronized data, three phases of the sit-to-stand motion were identified--phase 1, weight shift; phase 2, transition; and phase 3, lift. A consistent pattern of trunk and lower extremity motion was observed, and two distinct upper extremity movement strategies were identified. The onset of muscle activity occurred in the following order: erector spinae, rectus femoris, and vastus medialis (phase 1); biceps femoris, gluteus maximus, and rectus abdominus (phase 2). This characterization of the sit-to-stand motion for a small population of healthy elderly subjects serves as a basis for identifying problems in elderly patients who demonstrate difficulty getting up from a chair.