Body equilibrium at the end of gait initiation: importance of ankle muscular force as evidenced in clubfoot children

Abstract

This study investigates the importance of ankle muscular force and foot shape on body equilibrium at the end of a first step by means of a comparison between healthy children and children with unilateral clubfoot who showed Triceps surae atrophy. Subjects were asked to initiate gait at different velocities and to perform a few forward-oriented steps. In healthy children, there was a significant increase in the number of positive values of the centre of gravity vertical acceleration at foot contact (Z″HC) as velocity increased without any difference between the preferred and non-preferred stepping foot. These results indicated that ankle muscular forces from the leg of support intervene in braking the downfall of the body, as velocity and step length increase, and that this function does not depend on the subject's lateralization. In comparison with healthy children, clubfoot subjects showed a greater occurrence of low or negative Z″HC values when gait was initiated at a velocity greater than 0.8 m/s. However, except for two of them, there was no difference in Z″HC control between the steps initiated with the sound leg and those initiated with the affected leg. These results indicate that in unilateral clubfoot children, residual musculoskeletal impairment of one leg induces a deficit in equilibrium control as soon as step length needs a significant braking of the body's vertical fall. It is also shown that equilibrium is not limited to the gait period where the affected leg is the body's supporting leg but also when it is the stepping one. This could reflect a global alteration of the body scheme preserving symmetry in the control of both legs.