The prime mover of thigh extension against resistance is the:
a. Gluteus maximus
b. Gluteus medius
c. Biceps femoris
d. Semimembranosus

Verified step by step guidance

1. Step 1: Understand the action described in the problem, which is thigh extension against resistance. Thigh extension refers to moving the thigh backward, increasing the angle between the front of the thigh and the pelvis.
2. Step 2: Identify the muscles listed in the options and their primary functions. The gluteus maximus is known for powerful hip extension, the gluteus medius primarily abducts the thigh, the biceps femoris is part of the hamstrings involved in knee flexion and hip extension, and the semimembranosus is also a hamstring muscle involved in hip extension and knee flexion.
3. Step 3: Recognize that the term 'prime mover' refers to the muscle that is the main contributor to a specific movement, especially against resistance.
4. Step 4: Compare the muscles' roles in thigh extension. While the hamstring muscles (biceps femoris and semimembranosus) assist in hip extension, the gluteus maximus is the most powerful and primary muscle responsible for thigh extension against resistance.
5. Step 5: Conclude that the prime mover of thigh extension against resistance is the gluteus maximus, based on its size, strength, and primary function.

Key Concepts

Thigh Extension Movement

Thigh extension refers to the backward movement of the thigh at the hip joint, increasing the angle between the front of the thigh and the pelvis. This motion is essential in activities like standing up, walking, and running.

Prime Mover (Agonist) Muscle

The prime mover is the main muscle responsible for producing a specific movement. In thigh extension, the prime mover generates the majority of force to extend the hip against resistance.

Muscles Involved in Thigh Extension

Key muscles that contribute to thigh extension include the gluteus maximus, biceps femoris, and semimembranosus. The gluteus maximus is the largest and most powerful hip extensor, while the biceps femoris and semimembranosus are part of the hamstrings group assisting in this movement.