[Development of the gravity vector in normal walking. Muscular and kinetic correlations]

The vertical vector P which represents the body weight in a standing subject undergoes variations in the course of walking which merits study. This is the subject of this article. It is based on the numerical findings derived from work published on walking and is concerned with its displacement, the ground contact forces, muscular activity and expenditure of energy. A study using pressure transducers makes it possible to trace the progressive area of the gravity vector in the horizontal plane in the course of walking. At the same time, the progressive position of the centre of gravity in space can be registered and timed. The resulting trace is analogous to that obtained by a study of plantar pressures. The gravity vector is displaced in the course of walking like the clapper of a clock, suspended at the centre of gravity and passing successively in diagonal form in the four sectors of the horizontal plane defined by the axis of the walking and the frontal plane. In this displacement, its value varies steadily and cyclically. The trunk muscles, whose contraction has been studied clinically and by electromyography at the time of the different phases of walking are exactly those which can provide the mechanical compensation necessary for the displacement of the body weight vector. As to the time factor, it seems to show that, for a given subject, there exists, in relation to his weight and the height of the centre of gravity a speed of walking that corresponds to the minimum expenditure of energy.