During the concentric phase of the pull-up exercise, what action occurs at the glenohumeral joint?

In the concentric phase of a pull-up exercise, the primary movement at the glenohumeral joint is shoulder adduction. During this phase, as one pulls their body upwards toward the bar, the primary muscles responsible for this action, such as the latissimus dorsi and the teres major, work to bring the upper arm toward the body's midline. This movement aligns with shoulder adduction, wherein the arms are lowered from an outward position to a position closer to the torso.

Shoulder flexion would involve lifting the arm forward and upward, away from the body, while shoulder abduction refers to moving the arm away from the body's midline, both of which do not accurately describe the movements occurring during a pull-up. Additionally, shoulder extension involves moving the arm backward relative to the body, which also does not occur in the upward pulling motion of a pull-up. Thus, the correct identification of the action at the glenohumeral joint during this exercise is shoulder adduction.