Final answer:
The gluteus medius and gluteus maximus are the main muscles that regulate internal rotation of the hip, with the sartorius also contributing. The correct option is 5.
Step-by-step explanation:
The muscles that regulate internal rotation of the thigh at the hip joint include the gluteus medius and gluteus maximus, along with muscles like the adductor longus, adductor brevis, adductor magnus, and the pectineus. The gluteus medius is particularly involved in the stabilization and internal rotation of the hip when the hip is in a flexed position, which is essential during actions like walking.
While the gluteus medius can assist with internal rotation, the primary internal rotators are the muscles of the medial compartment such as adductor longus and gracilis. These adductor muscles, along with others in the medial compartment, are responsible for pulling the thigh inward, which represents the internal (medial) rotation of the hip joint.
The gracilis is also involved in this action; however, it functions mainly to adduct the thigh and flex the leg at the knee. Therefore, in the options provided, the muscles that regulate internal rotation are primarily the gluteus medius and the adductors. Hence, 5 is the correct option.