The long head of the biceps femoris also performs which action?

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The long head of the biceps femoris is a two‑joint muscle that crosses both the hip and knee, so it can extend the hip, flex the knee, and, when the knee is flexed, rotate the leg laterally. Its tendon inserts on the head of the fibula, placing the tibia on the outside of the leg during knee flexion and producing external (lateral) rotation. Dorsiflexion and plantarflexion are ankle movements and aren’t actions of this muscle, and medial (internal) rotation would be opposite to what this muscle tends to do when the knee is bent. So lateral rotation of the leg is the best, correct action.