Which statement correctly describes the relationship between agonist and antagonist during movement?

Which statement correctly describes the relationship between agonist and antagonist during movement?

• A. Antagonist lengthens, agonist shortens
• B. Antagonist shortens, agonist lengthens
• C. Both shorten
• D. Both lengthen

Answer: (A)

During movement, one muscle group (the agonist) shortens to produce the motion, while the opposing muscle group (the antagonist) lengthens to let that motion occur. The agonist pulls the joint in the desired direction, and the antagonist must relax or stretch so it does not oppose the movement. This is why the description of the antagonist lengthening as the agonist shortens best captures their dynamic relationship. For example, in elbow flexion the biceps (agonist) shortens to bring the forearm up, while the triceps (antagonist) lengthens to allow that bending without fighting the motion. If both muscles shortened, or both lengthened, the movement would be hindered or would not occur. Co-contraction can happen for stability in some tasks, but the simple, smooth movement pattern relies on the antagonist lengthening as the agonist shortens.

During movement, one muscle group (the agonist) shortens to produce the motion, while the opposing muscle group (the antagonist) lengthens to let that motion occur. The agonist pulls the joint in the desired direction, and the antagonist must relax or stretch so it does not oppose the movement. This is why the description of the antagonist lengthening as the agonist shortens best captures their dynamic relationship. For example, in elbow flexion the biceps (agonist) shortens to bring the forearm up, while the triceps (antagonist) lengthens to allow that bending without fighting the motion. If both muscles shortened, or both lengthened, the movement would be hindered or would not occur. Co-contraction can happen for stability in some tasks, but the simple, smooth movement pattern relies on the antagonist lengthening as the agonist shortens.