What is the action of the biceps femoris?

The main action of biceps femoris is the knee flexion and hip extension.

Explanation:

Biceps femoris muscle is a thigh muscle present in the posterior part of the body. This muscle has two heads of origin.

Biceps femoris is involved in the knee flexion. The kknee flexion decreses the angle between the femur and tibia. Biceps femoris is also involved in the hip extension. The hip joints are open during hip extension.