Which term describes the action of straightening a body part?

The term that accurately describes the action of straightening a body part is "extension." Extension refers to the movement that increases the angle between two parts of the body, effectively straightening them out. For example, when you extend your arm or leg, you are moving that limb away from your body or straightening out a bent position. This action is fundamental in many physical activities and is essential for maintaining proper movement and posture.

In contrast, the other terms relate to different types of movements. Bending typically refers to flexion, which is the act of decreasing the angle between two body parts, such as bending your elbow or knee. Flexion is specifically the movement that brings two body segments closer together. Rotation involves turning a body part around its axis, like rotating your head or torso. These movements are vital in various physical activities and play significant roles in understanding human anatomy and biomechanics.