On the Movement of Animals, Part Two

the destruction of the proposed proposition would follow from this very fact.

Chap. 1. Concerning the modes and mechanical operations by which the contraction of muscles can occur.

Since it is supposed that the action of a muscle is a contraction ordered toward lifting weights, and such a shortening ought to occur not from the rest of the parts but from their motion, by which, namely, they are brought closer to one another; and since such motion cannot be completed in muscles except by exercising a huge force so that the suspended weights can be lifted, and for the whole time during which the parts of the muscle are moved, softness persists in them according to the hypothesis, nor has hardness yet been induced: therefore, the huge force by which vast weights are lifted and the action of the muscle, which is its contraction, are exercised when they are still soft, before they are rendered hard—that is, before the parts of the muscle come to rest. For which reason, rest will not be the cause of the lifting of weights and the action of the muscle.

Nor, because the continuation of the suspension happens at a subsequent time, while the hardness of the muscle persists, can it be said that the energy of the rest of the muscle's parts is the cause of such suspension; because such action is an endeavor and a continuous impulse by which the moist—and therefore not hard—parts of the muscle are contracted by a certain laborious motive force; which is conjectured from the subsequent lassitude, when a tremulous motion follows from that struggle, by which the suspended weight is retained.