Subacromial impingement syndrome (SIS) is a common disorder of shoulder joint. SIS has been accounted for 44-65 % of all shoulder pain. It is believed that one important contributing factor is scapular dyskinesis. Patients with SIS demonstrates scapular dyskinesis, including decrease in upward rotation, scapular posterior tilt, and external rotation. Altered muscle activity of scapular muscles may contribute to scapular dyskinesis, such as increase in activity of upper trapezius, and decrease in activity of lower trapezius and serratus anterior. In addition to these changes in neuromuscular control, central nervous system may be re-organized in patients with musculoskeletal disorders. Evidence has been reported that center of gravity of motor mapping changes, corticospinal excitability decreases and inhibition increases in patients with shoulder injuries such as instability, rotator cuff tendinopathy and SIS. These corticospinal changes are believed to be related to chronicity of symptoms and lack of treatment effects.

Previous studies have applied many types of treatments to SIS, such as manipulation, taping, and exercises. However, most studies mainly focused on the outcomes of pain and function, few studies investigated changes in neuromuscular control following treatments. Yet, no study has addressed how corticospinal system changes following treatment in patient with shoulder injuries. Motor skill training, which has been widely used in training healthy subjects or patients with neurological disorders, has been shown to change corticospinal systems, including increasing excitability and decreasing inhibition. To our knowledge, no study has integrated the concepts of motor skill learning into a short-term treatment or investigated the effects of motor skill training on corticospinal systems in patients with SIS. The purposes of the study are to investigate the effects of short-term motor skill training on pain, neuromuscular control, corticospinal system in patients with SIS, and also to investigate whether changes in corticospinal parameters will be related to changes in pain, function and neuromuscular control.

Inclusion Criteria (patients with shoulder impingement) :

1. perform overhead exercise at least 4 hours a week

2. present type I or II scapular dyskinesis at rest or moving

3. pain at least two weeks

4. 3 of 6 impingement test present positive

   • Neer's impingement test: arm abduction overhead with shoulder internal rotation and thumb downward. If feel pain, then positive.
   • Hawkins-Kennedy impingement Test: arm lift to horizontal plane, elbow flexion to 90 degree. Tester put force on forearm toward shoulder internal rotation. If feel pain, then positive.
   • Empty can test: shoulder abduction with thumb down, then give a resistive force toward up. If feel pain, then positive.
   • Resistive shoulder external rotation test: elbow flexion to 90 degrees and do resistive shoulder rotation. If feel pain, then positive.
   • Rotator cuff tenderness test: tester put pressure on rotator cuff. If feel pain, then positive.
   • Painful arc: perform arm elevation. If feel pain during movement, then positive.

Inclusion Criteria (healthy people) :

1. perform overhead exercise at least 4 hours a week
2. no any symptoms or injuries on shoulder and neck

Exclusion Criteria:

1. Have a history of dislocation, fracture, or surgery of upper extremity
2. A history of direct contact injury to the neck or upper extremities within the past 12 months
3. A concussion within the past 12 months or a history of three or more concussions
4. Brain injury and neurological impairment
5. History of frequent headache or dizziness
6. Contraindications to the use of transcranial magnetic stimulation (TMS), assessed with a safety screening questionnaire, including pregnancy, history of seizure, epilepsy and syncope, having cochlear implant, having medal implant and taking anti-depressant medication.