Opposing pairs of muscles that move the same bone in opposite directions.
Opposing pairs of muscles that move the same bone in opposite directions. Muscles can pull when they contract, but they cannot push. So they are arranged in pairs to allow power to be exerted in both directions. An extensor muscle, such as the triceps in the human arm "opens" a joint, and the flexor muscle, such as the biceps, closes it.
Muscles can pull when they contract, but they cannot push. So they are arranged in pairs to allow power to be exerted in both directions. An extensor muscle, such as the triceps in the human arm "opens" a joint, and the flexor muscle, such as the biceps, closes it.