In the world of dreams the rules of reality do not necessarily apply. Each dream is unique and it's a direct link to the soul and spirit. Psychology provides its own theories on what dreams mean, but so did tradition and the study of dreams for thousands of years before any relevant science had developed.
Dream Meanings - Shoulder
To dream you have strong, muscular shoulders means you will receive help from someone and your work will go well, but if your shoulders are weak and slouching then expect problems at work that will be difficult to resolve.