Some biomechanical consequences of varying foot placement in sit-to-stand in young women.

The position in which the feet are placed prior to the start of sit-to-stand affects the distance to be moved by the body mass forward over the feet. The purpose of this study was to examine the effect of three foot placements, back, preferred and forward, on biomechanical features of the action. Six subjects were videotaped standing up from a seat with feet on a forceplate. XY coordinates and forceplate data were synchronised and kinematic and kinetic variables analysed. A forward foot placement significantly affected both the pre-extension and extension phases of the action. Under this condition, it was evident that body mass was moved the greater distance horizontally: i) by increasing the speed and amplitude of trunk flexion; and ii) by increasing the time over which the shank rotated forward at the ankle. Vertical movement of body mass was achieved largely by a 50% increase in peak moment of force at the hip. It is concluded that a forward foot placement would adversely affect the ease of standing up for individuals with leg muscle weakness and poor motor control. Since the altered biomechanical characteristics may place additional strain on the hip, patients should be cautioned to avoid standing up with feet forward after hip replacement surgery.