Biomechanics and muscular activity during sit-to-stand transfer.

In the present study 10 healthy subjects were measured, performing sit-to-stand transfers in a natural way. Starting position and speed of movement were standardized. Sagittal kinematics, the ground reaction force, and muscle activity of nine leg muscles were recorded. During sit-to-stand transfer the mass centre of the body was moved forward and upward. Based on the velocity of the mass centre of the body three phases were distinguished. In horizontal direction forward rotation of the upper body contributed to the velocity of the mass centre of the body, whereas extension of the legs contributed considerably in vertical direction. After seat-off most muscles were concentrically active, whereas the shortening velocity of the rectus femoris was very low. Thus hip and knee joints were extended and a relatively high knee moment was delivered to control the ground reaction force in a slightly backward direction. Co-contraction of hamstrings and rectus femoris in sit-to-stand transfer was judged to be efficient.