The principal features of maximal exertion in the sagittal plane

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Abstract
The postural stability diagram (PSD) is a plot of the vertical component of a manual force against the horizontal component. It may be used to assess the interactions of manual strength, frictional limitations at the feet and the forces demanded by a task. Data on human strength are presented in the form of postural stability diagrams. The observed features of maximal exertion, in all directions in the sagittal plane, are presented and analyzed. Measurements were made on men and women using 12 different combinations of hand and foot placement. Sex, the position of the hands and feet, and the direction of exertion were important determinants of strength. In a minority of conditions strength is limited by the distribution of body weight and the extent of the foot base. Centers of foot pressure were rarely located at the posterior limits of a subject''s anatomical foot base. In certain combinations of hand and foot placement, pronounced peak forces were observed for a narrow range of directions of exertion in the lift/push quadrant.