Participants will be recruited from outpatient clinic in National Taiwan University Hospital (NTUH) and also through general announcements in social media. Subjects will be undergoing physical examinations for eligibility by a physical therapist. Thoracic kyphosis angle, one inclinometer over 1st and 2nd thoracic spines, and another inclinometer over the 12th thoracic and 1st lumbar spines in relaxed standing with adopting a natural posture of the subject, is calculated by the summation of the angle recorded by two inclinometers. Participants will sign a consent form approved by the National Taiwan University Hospital institutional review boards. Participant characteristics will be collected by the assessor including age, gender, height, weight, dominant side, involved side, VAS (Visual Analogue Scale) pain intensity during arm movements, symptom duration and shoulder function. Shoulder function will be assessed by Flexilevel Scale of Shoulder Function (FLEX-SF), a self-administered questionnaire. The questionnaire was commonly used in shoulder pain patients to assess shoulder function with sufficient psychometric properties. Lower FLEX-SF score represents limited function.

Subjects will be randomly assigned into 2 groups (self-comfortable following forced tension and forced following self-comfortable tension groups) with 2 directions of strap in each tension wearing shoulder brace. Each subject has the assessment 2 times with 1-week interval. At the first, each subject will be assessed on PMI, SI, AD and SA with and without shoulder brace in resting position. Then the surface EMG electrodes and FASTRAK kinematic sensors will be attached to the subjects. Surface EMG electrodes will be placed on upper trapezius, middle trapezius, lower trapezius and serratus anterior of involved shoulder. Three electromagnetic sensors will be attached to the sternum, the flat bony surface of the acromion and the distal humerus via Velcro straps.

Then subject will be tested wearing shoulder brace with two tensions of strap (self- comfortable/ forced) under two directions of strap (paraspinal muscle/ diagonal orientation). Strap is applied from mid-level of thoracic spinal process to mid-point of clavicle on the tested side and then pulled downward diagonally back to the thoracic spinal process and then applied the same way in the other side. In general, strap had a cross on mid-thorax and ran through mid-point of clavicle and axillary two sides. For the strap tension, length of strap will be adjusted with buckles relative to original length of figure 8 by the experimenter. Self- comfortable tension of strap will be adjusted by subject's feedback with comfortable feeling as "please feel postural correction by shoulder brace without tight pressure". Accordingly, the self-comfortable tension of strap will be increased till forced tension of strap using buckles. Direction of strap will change bilaterally as upper part of shoulder brace is fixed at 2 points of shoulder brace .

Then subjects will be tested and familiarized with the arm movement with and without shoulder brace. To ensure that each subject perform arm movements at a standard speed, a metronome will be set as one beat per second. Subjects will be asked to elevate and lower arm by following three beats, respectively. Each subject will do task three times with or without shoulder brace in each session. After one week from the first assessment, each subject will be assessed again under another condition of strap tension according to their assignment groups.

Maximum voluntary isometric contraction (MVIC) of the subject will be collected after the testing session to prevent fatigue of the scapular muscles. The MVIC for upper trapezius muscle will be measured during resisted shoulder flexion. The subjects will be seated with shoulder flexion 90 degrees and resistance will be applied on the distal arm. For measuring MVIC of middle trapezius muscle, the subjects will lie prone with testing arm at 90 degrees of abduction. For measuring MVIC of lower trapezius muscle, the subjects will lie prone with testing arm at 120 degrees of abduction in line with muscle fibers. Resistances will be applied to against further elevation. For measuring MVIC of serratus anterior muscle, the subjects will be seated with arm elevated at 135 degrees. Resistances will be applied to distal upper arm against further elevation. The MVICs will be collected for 5 seconds for 3 trials, with a 1- minute rest interval between each trial.