On the Movement of Animals, Part Two

by the same cord AEG, are quadruple the resistance RS, or the weight Z, which was to be shown, etc.

PROPOSITION V.

Because machines are of such a nature that they cannot be contracted unless they are first distracted and subsequently abandoned by the distracting power: therefore, as long as the muscular chain is not distracted, it will not be contracted, for it will persist in its natural elongation. Secondly, if it is distracted by some weight, as long as the weight is attached, an equilibrium is conserved, and therefore it is at rest; wherefore it is impossible for the muscle fibers to be contracted at the animal's will by the simple force of the machine. But the contraction can only occur when some external force, whether by a cord or another organ, is applied, which can overcome in double proportion not only the resistance of the attached weight but also that by which the machine resists restriction; namely, it will be quadruple the attached weight, which excess ought to be multiplied as many times as there are machine-elements contained in the chain of the muscle. Therefore, it is so far from being the case that the force of the machine can lift attached weights that, on the contrary, it impedes the elevation of the same, since it resists its own contraction.

Furthermore, the force by which the fibers of the machines are contracted of themselves is equal to the contrary power of the antagonistic muscle