Which plane divides the body into upper and lower segments?

The transverse plane is the correct choice because it is the anatomical plane that divides the body into upper (superior) and lower (inferior) segments. This plane runs horizontally across the body, creating a cross-section and allowing for movements that involve rotation, such as twisting actions of the trunk or limbs.

Understanding the role of the transverse plane is critical for fitness instructors, as it helps in designing exercises that effectively engage various muscle groups involved in rotational movements. In contrast, the sagittal plane divides the body into left and right segments, focusing on forward and backward movements. The frontal plane separates the body into anterior (front) and posterior (back) sections, facilitating lateral movements. The longitudinal plane is not a standard anatomical reference but can be understood as any plane that runs parallel to the long axis of the body. Therefore, the definition and application of the transverse plane are essential for comprehending human anatomy and movement dynamics.