The Elbow as a Lever: Why Pulling Beats Pushing
The arm muscles argued by the science of weights, and the added force of the whole body
The text treats the muscles of the upper arm (the 'aiutorio') as levers: the extensor lies behind the bone and the flexor in front. Invoking the ninth proposition of the medieval De ponderibus, it argues that of two equally strong muscles the one fixed farther from the pole of the elbow, labelled a, is the more powerful, so the front muscle h c outpulls the rear muscle h b. It distinguishes 'simple' force from 'compound' force, which adds the weight of the body and the power of the back and legs, as when one man pushes and another pulls a column, and opens the question of whether pulling or pushing is stronger. The page carries a labelled diagram of an arm bone (h, b, c, a) and a small crouching figure.
On this page
The elbow argued by the science of weights (De ponderibus)
By the ninth proposition of the De ponderibus, among weights of equal power the one more remote from the pole of the balance shows itself the more powerful. Since muscles h b and h c are of equal power, the front muscle h c is the stronger, because it is fixed to the arm at c, farther from the pole of the elbow a than is b, which lies on the far side of that pole.
Extensor behind the bone, flexor in front
Of the bone called the aiutorio the two muscles lie one behind the other: the one born behind extends the arm, and the one in front bends it.
Compound force adds the weight of the whole body
Simple force is that of the arm alone; compound force is when an operation of the arms is joined to a second power, the weight of the person and of the legs together with the force of the back, as in pulling and pushing. Much greater power lies in pulling than in pushing, because in pulling the power of the muscles is added.