Answer
An example of movement by muscle action is the flexing of the forearm by contraction of the biceps brachii. In this action the elbow joint serves as the fulcrum (F). The effort is applied by contraction of the belly of the biceps brachii. This muscle has its origin on the scapula and inserts on the radius; the effort is applied at the insertion of the muscle on the radius(E). The resistance (R) supplied by the weight of the forearm plus any load that may be in the hand. This arrangement of the factors that determine the classes of levers is of the order FER-- Effort between Fulcrum and Resistance.
Work Step by Step
The FER arrangement means that the flexing of the forearm at the elbow joint classifies as a movement in the Third class or Third Order of levers.
