What movement do muscles that pass posterior to the spine primarily cause?

Muscles that pass posterior to the spine primarily contribute to extension. This is due to their anatomical positioning; when muscles are located at the back of the spine, their contraction pulls the vertebrae in a direction that increases the angle between the body segments, effectively straightening the spine.

For example, the erector spinae group is a major muscle group that runs along the posterior side of the spine and plays a crucial role in maintaining an upright posture and extending the back. When these muscles are activated, they help lift the torso and straighten this region of the body, allowing for movements such as standing tall or arching backward.

Understanding this concept is vital for anyone studying Pilates, as many exercises focus on spinal alignment and engagement of these muscle groups to promote proper movement patterns and prevent injury.