Analysis of relationship between trunk movement and joint moment during sit-to-stand motion

Abstract

BACKGROUND: Standing from a seated position is a common activity that is performed many times during the course of day and is a skill that indicates the functional level of a person. In this motion, flexion motion of the trunk is an indispensable movement. Then, the limitation of the motion alters the course of center of mass and influences lower extremity kinetics. PURPOSE: Author aimed to analyze lower extremity muscle force under restricted trunk flexion movement in sit-to-stand (STS) motion using biomechanical model. METHODS: Ten healthy adult subjects performed the STS motion in 2 different manners: 1) free STS motion as usual activity, 2) STS motion with diminished trunk flexion. Kinematic and kinetic data were gathered using a three-dimensional motion analysis system (Oxford Metrics VICON370) with force plates. RESULTS: The author recognized significant influence on the magnitude of lower joint moment by the restricted trunk flexion. Strongest correlation between the amount of the joints moment and trunk flexion angle was found at a period of the buttock off the chair and of the maximal hip extension. During the STS motion with less flexion of trunk, compared to the free STS motion, the hip extension moment became large, and the moment of knee extension was lessened. The maximal knee extension moment appeared after the hip extension moment reached its maximum. More, the center of mass moved backward. The load of the knee extensors increased. And more, the correlation between movement of head, neck and upper trunk and moment of knee extension was recognized. CONCLUSIONS: In STS motion, the influence of trunk flexion angle was detected in all the lower extremity joint moments, and it was induced that the center of mass moved backwardly. The author confirmed that limited movement of trunk and trunk segmental movement decreased the load of the knee increased.