We report the case of a patient with global rotator cuff tear who had difficulty in drinking soup using the left hand. Active flexion of her shoulder was more restricted than shoulder abduction. Excessive abduction was required to maintain the motion of keeping the cup at the height of the lips when the patient used her left hand. An electromyogram revealed excessive activities in the trapezius and deltoid muscles and low activity in the serratus anterior muscle. The function the patient's scapular girdle muscles was normal; however, upward rotation of the scapula was restricted. Physical therapy was administered mainly to improve the upward scapular rotation. Subsequently, active flexion improved. Stabilizing the scapular girdle and training the serratus anterior muscle resulted in an improvement in the motion of keeping the cup at the height of the patient's lips while drinking soup with her left hand flexed. The improvement in the scapular girdle function for flexion was useful for improving the shoulder function of our patient with global rotator cuff tear.