Which of the following best describes an action happening in the sagittal plane?

The correct choice describes an action that occurs in the sagittal plane, which divides the body into left and right halves. Movements in the sagittal plane include flexion and extension, which are characterized by forward and backward movements.

Bending forward at the waist is an example of flexion, which happens in the sagittal plane as it involves decreasing the angle between the body parts. This is a common movement that reflects how the body moves in a forward direction while maintaining this division.

The other options involve movements that occur in different planes of motion. For instance, rotating the torso is a rotational movement that occurs in the transverse plane. Raising an arm to the side involves abduction, which occurs in the frontal plane, and lifting a leg horizontally also represents a movement in the frontal plane, not in the sagittal plane. Understanding the planes of motion is crucial for analyzing different types of exercises and movements in physical training and rehabilitation.