Leonardo’s famous sketch was made as a study of the male human proportions. It was based on text written by the ancient Roman architect Vitruvius.
The multiple viewpoints seen in the drawing serve to illustrate that there are no universal set of proportions for the human body.
Vitruvius states that the centre of the body is the navel, but Leonardo’s sketch shows that this depends on the position of the arms and legs, and when the figure is in the standing position, the centre of gravity is actually lower than the navel.