Which muscle is responsible for flexing and rotating the vertebral column?

The rectus abdominis is the correct choice because it plays a crucial role in flexing the vertebral column, particularly when performing movements like crunches or sitting up from a lying position. This long, flat muscle extends vertically along the front of the abdomen, and its primary function is to flex the lumbar spine and assist in bending forward.

Additionally, the rectus abdominis helps with rotation to some extent, particularly when working in conjunction with other muscles, such as the obliques. These functions are vital in Pilates, where core stability, flexion, and rotation are emphasized in various exercises.

In contrast, while the biceps brachii is a muscle of the upper arm mainly responsible for elbow flexion and forearm supination, the trapezius muscle primarily facilitates movements of the shoulder and neck, and the latissimus dorsi contributes to the movement of the shoulder and upper arm but does not directly affect the flexion or rotation of the vertebral column.