Gait and balance disorders are important public health problem necessitating studies to try to prevent falls. Many studies have dealt with spatiotemporal gait parameters or balance during quiet standing (posturography). Nevertheless, falls occurred predominantly during gait, and rarely during quiet standing. We have developed a tool to measure balance during gait : the braking of the center of mass (CM), a biomechanical parameter obtained from the vertical velocity of the CM recorded with a force plate.