Final answer:
The hamstrings flex the leg at the knee joint and extend the thigh at the hip joint.
Step-by-step explanation:
The hamstrings are a group of muscles located on the back of the thigh. They have different actions at the knee and hip joints.
At the knee joint, the hamstrings act to flex the leg. This means that they bring the lower leg closer to the back of the thigh. The three muscles that make up the hamstring group are the biceps femoris, semitendinosus, and semimembranosus.
At the hip joint, the hamstrings act to extend the thigh. This means that they bring the thigh backwards. In addition to thigh extension, the hamstrings also aid in twisting the thigh outward. The primary muscle that performs hip extension is the gluteus maximus.