The unilateral superman is a great shoulder mobility and stability drill for the scapula. The scapula is controlled by many supporting stabilizers that rarely or sometimes never explore their full active range.
The scapula needs to initiate movement prior to the shoulder. This “timing” is often lost particularly in internal rotation and active extension, they are our least used ranges. When the scapula and the shoulder are not in sync, nerves and delicate tissue fibers can be susceptible to damage or irritation.
This is an exercise where less is more. You’re attempting to relearn or possibly learn for the first time proper shoulder mechanics. It should be done slowly, with focus and good breathing in order to maximize it’s potential. This should feel “rough” It should not be easy. Prioritize this as a movement prep exercise 🌳