Too much stress -- or too many fastballs -- can cause partial tears and swelling in the tendons of the rotator cuff. Abrupt stress may even cause one of the tendons to pull away from the bone or tear in the middle of the tendon.o diagnose a rotator cuff tear, your doctor will give you a thorough physical exam. He or she will want you to move your arm in different directions to see what causes pain. In addition, your doctor might want to order the following tests: 1  X-ray of the shoulder with some special views.
In rare cases, generalized muscle weakness may be caused by another health problem, such as: 1  A problem with the minerals (electrolytes) found naturally in the body, such as low levels of potassium or sodium. 2  Infections, such as a urinary tract infection or a respiratory infection.
Potential Causes of Muscle Weakness. There are many possible underlying causes for muscle weakness. Possible causes include: 1  chronic fatigue syndrome. 2  muscular dystrophy. 3  Graves disease. 4  Guillain-Barre barrÃ©. 5  syndrome. 6  hypothyroidism (hypotonia lack of muscle, tone usually present at). 7  Birth Louâgehrig s.  disease