Muscle Synergy Analysis of Human Standing-up Motion in Different Seat Heights and Speeds

In order to understand human motor function, it is necessary to clarify how humans achieve adaptive motions regarding to external environment or their own purpose. This study analyzes human standing-up motion in different chair seat heights and motion speeds using muscle synergy analysis to find important modules to achieve the movement. Muscle synergy is determined from measured eight muscle activations (n = 10), and relationship between muscle synergy and body kinematics is clarified. As a result, invariant three muscle synergies were found in human standing-up motion regardless of different seat heights and motion speeds. On the other hand, amplitude and duration of time-varying activation of muscle synergies were properly adujusted to enviromental change. Moreover, it was observed that time-varying activations were strongly corresponded to characteristic kinematic event of standing-up motion. This result implies that humans can achieve the adaptive standing-up motion mainly by controlling time-varying activation of three muscle synergies.