Which movement cannot be primarily caused by the hamstring muscle group?

The hamstring muscle group primarily consists of three muscles: the biceps femoris, semitendinosus, and semimembranosus. These muscles are primarily responsible for flexing the knee and extending the thigh at the hip joint.

Adduction of the thigh, however, primarily involves different muscle groups, particularly the adductors located in the inner thigh. The hamstrings do not play a significant role in this movement, as their main functions are not related to bringing the thigh towards the midline of the body. Instead, they are more involved in bending the knee and extending the hip.

Therefore, when considering the specific functions and actions of the hamstring group, adduction of the thigh is the movement that cannot be primarily caused by them, making it the correct choice in this scenario.