Muscle Pairs (AQA A Level Biology): Revision Note

Antagonistic muscle action

• Skeletal muscles enable movement when they exert a pulling force on the rigid, incompressible skeleton

  • Muscles are connected to bones via tendons, which do not stretch when a muscle is contracting and pulling on a bone

• Because muscles can only pull, and cannot push, they often act in pairs known as antagonistic pairs

  • In an antagonistic pair, one muscle will pull the bone in one direction, and the other muscle will pull the bone in the opposite direction

• The biceps and triceps muscles in the arm are an example of an antagonistic pair:

  • To raise the lower arm:

    • the biceps contracts and the triceps relaxes

    • the bone of the lower arm is pulled upwards and the arm bends at the elbow

  • To straighten the arm:

    • the triceps contracts and biceps relaxes

    • the bone of the lower arm is pulled down and the arm straightens