Muscle in action, illustration

Illustration showing an outline of a shoulder, arm, and hand, the hand holding a ball, and the elements of the mechanics of the action of lifting the ball. The power (P) is supplied by the contraction of the biceps muscle, attached to the shoulder by two heads and fixed below to the radius, or outer forearm bone. The weight (W) is in the hand , and the fulcrum (F) is at the elbow-joint. This is a lever-action with the biceps power being applied between fulcrum and weight, a lever of the third order. Above the hand, II, the tiptoe illustration is of a lever of the second order, where the weight (W) is applied between the fulcrum (F) and the power (P). The power is supplied by the great calf muscle, the weight between transmitted down the bones of the leg. The illustration is from The Household Physician, 1908., by SHEILA TERRY/SCIENCE PHOTO LIBRARY