What type of muscle action primarily occurs at the elbow joint for flexion?

The primary muscle action that occurs at the elbow joint during flexion is indeed flexion. Flexion is the movement that decreases the angle between two body parts, in this case, bringing the forearm closer to the upper arm at the elbow joint. During this action, muscles such as the biceps brachii and brachialis contract to pull the forearm upwards, effectively bending the elbow.

The other options—extension, adduction, and abduction—represent different types of movements. Extension increases the angle between body parts, which is the opposite of flexion. Adduction refers to movement toward the midline of the body, while abduction involves movement away from the midline. These actions do not pertain to bending at the elbow, which is specifically described by flexion. Thus, flexion correctly identifies the action that primarily occurs at the elbow joint during this movement.