Final answer:
The latissimus dorsi muscle is responsible for shoulder extension in the sagittal plane, a movement that helps to move the arm backward.
Step-by-step explanation:
The latissimus dorsi muscle produces shoulder extension primarily in the sagittal plane, which divides the body into left and right parts. This muscle is one of the two axial muscles responsible for moving the humerus, with the other being the pectoralis major.
The latissimus dorsi is a large, triangular muscle located on the lower back, and during shoulder extension, it helps to move the arm backward from the anatomical position.