Now, here's a little curve ball. Would you ever think that your breathing style would have the same detrimental effects? When someone takes shorter breaths throughout the day, secondary respiratory muscles are used. These secondary muscles are basically all the muscles around the neck (scalenes, sternocleidomastoid, upper traps, levator scapula). This results in overuse that makes deep neck muscles weak which then lead to a chain of events in the shoulders.
What muscles SHOULD be used? Funny you should ask. Here are a few.