Contrapposto: how a figure's sides change when it stands on one foot
The navel and member stay level while the shoulder line tilts over the supporting foot
A sketch of a male torso and standing leg, divided by a vertical axis from head through the supporting foot, carries letter-labels: the shoulders d and b, a transverse line a above the navel, and e and c above the sex. Below it a schematic of a bent central line with three transverse lines a, b and c abstracts the same idea. Leonardo explains the geometry of contrapposto: as one side shortens in the pose the opposite side lengthens by as much, while the navel and virile member never change height; because the body poses over one foot, the shoulder line leaves the perpendicular and the transverse lines dip lower on the standing side.
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One side shortens as the other lengthens
As much as side d a of the nude diminishes because of the pose, so much does the opposite side increase beyond its measure. The navel never changes its height, nor does the virile member, because the supporting foot becomes the center of the weight.
The transverse lines a, b, c dip toward the standing side
When the figure poses on one foot, the middle of the shoulders comes over that foot and the central line bends so its upper end lies above the supporting foot; the transverse lines, held to equal angles, drop lower on the side the figure stands on, as shown at a, b and c.