How do the hamstrings function concerning joints?

The hamstrings are a group of muscles located at the back of the thigh, and they play a significant role in the movement of both the hip and knee joints. These muscles are primarily composed of three individual muscles: semitendinosus, semimembranosus, and biceps femoris.

When the hamstrings contract, they perform several functions. One of their main roles is to facilitate knee flexion, which means they help bend the knee joint when activated. Additionally, the hamstrings are involved in hip extension, which is the movement of the thigh backward, as seen during activities like walking, running, or climbing.

Because the hamstrings span both the knee joint and the hip joint, they are considered biarticular muscles, meaning they affect the movement of two joints. This unique anatomical positioning allows them to contribute to a variety of movements involving both joints, making them crucial for activities that require coordination and balance between hip and knee actions.

Thus, the correct answer highlights that the hamstrings cross both the knees and hip joints, which is essential in understanding their functional significance in movement and stability of the lower extremities.