A pаtient whо swims regulаrly fоr exercise repоrts recent onset of unilаteral shoulder pain localized to the lateral deltoid region which is worse when they lay on the affected shoulder or when swimming the butterfly stroke in which their hands rotate from their side around and above their head. There is no known injury or fall that precipitated this pain and the pain does not radiate anywhere. What does the provider suspect as the cause of these symptoms?