During the upward phase of a pull-up (with narrow grip and a supinated grip), the glenohumeral joint is moving from a position of to a position of extension.

Flexion

Explanation:

The glenohumeral joint is a joint formed between the scapula and the humerus is the shoulder. This type of joint is formed between a ball and a socket.

During pull up exercise in which the body is suspended with the help of hands and then pulled up with the force.

This pulls up changes the position of the elbow as the elbow bents that are in flexion as it decreases the angle between two bones and then extends as the angle increases. This repeated flexion and extension of the joint or bones is done during the pull-up.

Thus, flexion is correct.