According to Leonardo's preview in the accompanying text, written in mirror writing, it was made as a study of the proportions of the (male) human body as described in Vitruvius. The text is in two parts, above[a] and below[b] the image.
The first paragraph of the upper part reports Vitruvius: "Vetruvio, architect, puts in his work on architecture that the measurements of man are in nature distributed in this manner, that is: a palm is four fingers a foot is four palms a cubit is six palms four cubits make a man a pace is four cubits a man is 24 palms and these measurements are in his buildings". The second paragraph reads: "if you open your legs enough that your head is lowered by one-fourteenth of your height and raise your hands enough that your extended fingers touch the line of the top of your head, know that the centre of the extended limbs will be the navel, and the space between the legs will be an equilateral triangle".
The lower section of text gives these proportions: the length of the outspread arms is equal to the height of a man from the hairline to the bottom of the chin is one-tenth of the height of a man from below the chin to the top of the head is one-eighth of the height of a man from above the chest to the top of the head is one-sixth of the height of a man from above the chest to the hairline is one-seventh of the height of a man. the maximum width of the