Final answer:
The iliopsoas, composed of the psoas major and iliacus muscles, is the muscle that inserts onto the lesser trochanter of the femur. The gluteus minimus, gluteus medius, and other gluteal muscles insert on the greater trochanter or other parts of the femur. The correct option is iliopsoas.
Step-by-step explanation:
The muscle that inserts onto the lesser trochanter of the femur is the iliopsoas. This muscle group is composed of the psoas major and the iliacus muscles.
The gluteal muscles, which include the gluteus minimus, gluteus medius, and gluteus maximus, are primarily responsible for extending, abducting, and rotating the femur. However, they do not insert on the lesser trochanter. The largest of these is the gluteus maximus, which inserts into the gluteal tuberosity of the femur and the iliotibial tract. The gluteus medius and gluteus minimus insert on the greater trochanter of the femur, not the lesser trochanter.
The iliopsoas is a powerful hip flexor, and due to its position, plays a critical role in maintaining posture and facilitating movements such as walking and running. It originates from the lower back and the ilium (part of the hip bone) and inserts onto the lesser trochanter of the femur, allowing it to execute the primary action of hip flexion.