Final answer:
Muscles that act on the knee joint exhibit two actions: agonists and antagonists.
Step-by-step explanation:
When it comes to the knee joint, muscles can exhibit two actions. For example, the quadriceps femoris muscles in the anterior compartment of the thigh are activated to extend the knee, and they are called the agonists of knee extension. On the other hand, the hamstrings muscles are activated to flex the knee joint, which makes them the antagonists in this action.