What are the two main actions exhibited by muscles that act on the knee joint?

The two main actions exhibited by muscles that act on the knee joint are flexion and extension. Flexion refers to the bending motion at the knee, whereby the angle between the thigh and the lower leg decreases, such as when you bring your heels towards your buttocks. Extension, on the other hand, is the straightening motion where the angle increases, allowing the leg to move away from the body in a straight line, like when you kick your leg out straight from a bent position.

These two actions are essential for various activities such as walking, running, and jumping, as they allow for the full range of motion needed in the knee joint. Muscles like the quadriceps are responsible for extension, while the hamstrings facilitate flexion. Understanding these primary movements is crucial for evaluating knee function and addressing injuries related to this joint.