Joints and Levers

Common actions of the human body can be described in terms of the simple machines with application so the concepts of force and torque.

The lever system formed by the elbow in the example shown is called a third class lever because the lever arm for the biceps muscle is less than the lever arm of any force downward on the hand. The force in the biceps is much greater than that of any object carried in the hand. But there are times when such a lever is useful, as in throwing a ball. The speed of a ball leaving the hand is much higher than the speed of movement at the point of contact of the muscle.