The effects of the lower extremity joint motions on the total body motion in sit-to-stand movement

Objective. The purpose of this study is to investigate the effects of lower extremity joint angular motions on the whole body linear motions in a sit-to-stand movement using a biomechanical model that describes the whole body linear velocity vector as functions of lower extremity joint angular velocities. Design. Two-dimensional video analysis of whole body and joint kinematics. Background. A biomechanical model that describes the whole body linear motions as functions of lower extremity joint angular motions is needed to provide clinically relevant information in clinical services and scientific research. Methods. The linear velocity vector of the whole body motion during the sit-to-stand movement was partitioned into horizontal and vertical components and expressed as functions of lower extremity joint angular velocities for 10 healthy subjects. The coefficient of joint contribution to the whole body linear velocity vector was determined for each joint in each direction. Results. The ankle and hip angular motions are critical to the development of the forward horizontal velocity of the whole body during the sit-to-stand movement. The knee and hip angular motions are critical to the development of the upward vertical velocity of the whole body during the sit-to-stand movement. Conclusions. The hip, knee, and ankle joint angular motions have various roles in whole body motions in different directions of the sit-to-stand movement.