Which muscle group is targeted by the supine exercise with hands behind knees?

The correct answer, which identifies the targeted muscle group as the erector spinae, is based on the nature of the exercise described. The supine position with hands behind the knees often implies a movement that emphasizes the extension of the spine or stabilization of the core, both of which are primarily facilitated by the erector spinae muscles.

These muscles run along the length of the spine and are crucial for maintaining posture, extending the back, and providing support during various movements. When performing exercises in a supine position and possibly involving leg movements or stabilization with the arms, the erector spinae engage significantly to counteract gravity and stabilize the body.

In contrast, while the obliques are involved in rotational and lateral movements of the trunk, the hamstrings are primarily responsible for knee flexion and hip extension, and the trapezius is primarily associated with movements of the shoulder and neck. Thus, these muscle groups are not primarily engaged in the described supine exercise with hands positioned behind the knees.