In short, the vacuous definition of a triangular space with un­de­fined ver­ti­ces, between two asymmetric legs with different angles, de­ter­mines a tech­ni­cal­ly unacceptable puzzle; as long as it has a reason for being.

It is the legs that should form the triangle, equi­lat­er­al and large enough to reach with the feet at the actual base vertices, the largest circle.
But whatever equi­lat­er­al triangle could be, the dis­tance be­tween the tri­an­gle's base, in­scribed into the cir­cle, and the base of the squ­are, where the man stands, is said to be 1­/14 of the height of man and square.
Nonetheless, the decrease of the body height 1/14, from the square base to the base of the best equilateral triangle obtainable, does not match in this draw­ing – unless we trace the legs with their true len­ght [down to the yel­low cir­cle] – in which ca­se the dis­tance is exactly 1/14 of the height of the man and the squ­are itself! (PDF)
Here's a good reason to be finicky.

  • Evidently, this is not what Leonardo represented; but are we sure he was not aware of it? how could he know so well this ratio, without hav­ing chec­ked it directly and specifically?
Too much precise to be a case, this betrays that Leonardo measured this ratio by a real man or tool, but he choosed to sacrifice this matter of fact for an more powerful, erratic symbolism, the worldly ‘Canon of Pro­portions’.

“This image provides the perfect example of Leonardo's keen interest in proportion…
Won't anybody wonder how that greatest anat­o­mist and engineer could compromise his sketch, indulging in such kind of mis­takes by un­scho­oled?

“This work was not a portrait as much as a diligent depiction of a perfect male form designed by math, not shaped by life.…”
Strange ways indeed of uni­ver­sal­iz­ing the pro­por­tions of the ideal man, as all scholars acclaim, by whom "imagined the world en­tire­ly governed by mechanical principles…"!

“Specialists from the Imperial College of London analyzed The Vitruvian Man and found that the drawing shows a hernia in the groin (left). They believe Leonardo based his drawing in the corpse of a man that may ha­ve died of this.”
If so, this could confirm the above supposition; but it just remains to ask why no one among these specialists have noticed at least that they were facing four legs with the two abducted shorter, and four arms of which the two rotated were drawn longer.

“The fact that da Vinci studied detailed dissections of the human form is quite a well known one. This internal knowledge of each organ, each sinew, muscle and bone is something that governs the position of every arc and line in this illustration.”. Or rather, that denounces the hoax.

The earth's history of art is full of beautiful portraits and frescoes, in­clud­ing those of Leonardo; but when one ventures into the con­struc­tion of a sym­bol that goes beyond the pictorial and even scientific dimension, an emblem that should bind the physical and spiritual factors of the human being in a unique symbolic matrix, he must be well aware of what he is pro­duc­ing, since it is intended – as can be seen – to dra­mat­i­cal­ly in­flu­ence the minds and hearts, i.e. the culture of people over time; and here what should have been a seal turned into a cage, just a reductive media.

The same goes for all those who promote it and exalt it… without see­ing. The excerpts above are just a few citations; you can scan tens of ready made cloned articles like these through any search engine.