During shoulder medial rotation up to 60° in supine position, the scapula forward tilts or elevation occurs, difficulties in breathing, performing difficulties, unable to perform 60° medial rotation, glenohumeral anterior translation, fatigue, the need of external feedback and external support.

During shoulder medial rotation up to 60° in supine position, no scapula and glenohumeral compensation, easy to breathing and perform 60° medial rotation without external feedback and external support.

The subject performed upper extremity D2 diagonal exercise with Thera-band at kneeling position to simulate the arm movement of a volleyball spike. The movement is paced by a metronome at one beat per second, with one movement per beat. If participants could not keep up or become too fatigued, they are allowed to rest for 15 seconds before continuing.

The subject was defined as fatigued, and the fatigue activity was stopped, only when all three of the following cumulative conditions were met:

1. Until the number of repetitions in that set was less than 50% of the repetitions performed in the first set.
2. Using the Rating of Perceived Exertion (RPE) on a 6-20 scale, until the subject's RPE was greater than or equal to 15.
3. If this maximum strength showed a decrease of 25% or more compared to the maximum strength measured before the fatigue activity.

The kinematics is assessed using an electromagnetic motion tracking system (VIPERTM, Polhemus, USA) to measure the glenohumeral elevation, horizontal abduction/adduction, internal/external rotation, and scapulothoracic retraction/protraction, upward/downward rotation, anterior/posterior tilt during spiking movement. During the test, participants performed 3 times of cross-body spikes, with 15 seconds of rest between each trial.

Data were collected at the end of the arm cocking (maximal shoulder horizontal abduction) and at ball-contact (maximal footswitch signal), and reported as mean values for each trial. (unit of measure: degree, °)

The muscle activation amplitude of the serratus anterior, upper trapezius, lower trapezius, middle deltoid, infraspinatus, and pectoralis major during spiking movement. During the test, participants performed 3 times of cross-body spikes, with 15 seconds of rest between each trial.

Data were collected in the arm cocking phase (from minimal shoulder elevation to the shoulder maximal horizontal abduction) and the acceleration phase (from maximal shoulder horizontal abduction to the ball-contact), and reported as mean values for each trial. (unit of measure: percentage, %)

The mean power frequency of the serratus anterior, upper trapezius, lower trapezius, middle deltoid, infraspinatus, and pectoralis major during spiking movement. During the test, participants performed 3 times of cross-body spikes, with 15 seconds of rest between each trial.

Data were collected in the arm cocking phase (from minimal shoulder elevation to the shoulder maximal horizontal abduction) and the acceleration phase (from maximal shoulder horizontal abduction to the ball-contact), and reported as mean values for each trial. (unit of measure: hertz, Hz)

The subacromial structures is assessed using a diagnostic ultrasound system (SONIMAGE MX1 Ver. 1.10, Konica Minolta, Inc., Tokyo, Japan) to measure the acromio-humeral distance (AHD, from the lateral inferior edge of the acromion perpendicular to the humerus), supraspinatus tendon thickness (SST, from the subacromial-subdeltoid bursa perpendicular to the humerus), occupation ratio (OR, dividing SST by AHD). During the dynamic evaluation, participants performed 3 times of arm elevation to 90° and returning to the neutral position at scapular plane. During the static evaluation, participants performed 3 times of arm elevation to 60° at scapular plane.

Data of dynamic evaluation is collected at 0° elevation and at the greater tuberosity of the humerus is aligned under the lateral inferior edge of the acromion. Data of static evaluation is collected at 0° elevation and 60° elevation. Data reported as mean values for each trial. (unit of measure: millimeter, mm)