The goal of this clinical trial study is to determine efficacy of adding cervical stabilization exercises (CSEs) to conventional physical therapy (PT) program on pain severity, shoulder function disability, kinesiophobia, shoulder range of motion (ROM), isometric muscle strength and upper limb (UL) functional activity in closed kinetic chain in patients with SIS. The main questions it aims to answer is:

What are the effects of adding cervical stabilization exercises to a conventional physical therapy program in the management of shoulder impingement syndrome? Researchers will compare two groups: one group will receive CSEs beside the conventional PT program to the another group will receive the conventional PT program.

Shoulder impingement syndrome is a mechanical compression of the subacromial structures; specifically the subacromial bursa, rotator cuff, and long head of biceps tendons in the subacromial space. There are painful arm motions and functional restrictions.

The treatment of SIS focuses on improving pain and upper limb (UL) functions. Conservative treatments are effective in stages I or II of SIS.

Conservative treatments include non-steroidal anti-inflammatory drugs, corticosteroid injections, and exercise therapy such as strengthening for RC, and scapular muscles, stretching , proprioceptive neuromuscular facilitation (PNF), range of motion (ROM), and scapular stabilization exercises.

Cervical stabilization exercises (CSEs) can improve cervical spine stability, flexibility, muscular strength and endurance, and joint position sense. Shoulder stability extends beyond the shoulder joint as the head, neck, and shoulder are interconnected through muscles, tendons, and fascia.

Alteration of spine alignment leads to change mechanics of the shoulder. Forward head posture (FHP) can cause abnormal scapular orientation (internal rotation, elevation, and anterior tilting), decrease shoulder muscle strength, ROM, and increase humeral head translations that may predispose an individual to SIS. Also, increase thoracic kyphosis may cause increase scapular anterior tipping and retraction.

Crucially, the proper action of key scapular muscles, like the trapezius, requires the correct orientation of the cervical spine. This stability is achieved by the deep neck flexors (DNFs)-specifically the longus capitis and longus colli- which act as essential stabilizers for maintaining proper posture of the head and neck. Delayed timing of DNFs was shown to compromise spinal control during upper extremity function. Also, increased DNFs strength can enhance electromyographic (EMG) activity of scapular muscles (SA, UT, and LT).

One possible mechanism to describe the effect of CSEs in reducing pain is that stimulation of mechanoreceptors, including the muscle spindle and proprioceptors of joints. Signals from these receptors cause the release of endogenous opioids and beta-endorphins from the pituitary gland. Another possible mechanism of pain improvement is that the effect of these exercises in improving the coordination between the recruitment of the superficial and deep neck muscles. However, up to authors' knowledge, studies investigating the specific effects of adding CSEs to conventional SIS treatment are insufficient.

Inclusion Criteria:

• Male and female patients with unilateral SIS.
• Age is 20-40 years old.
• Presence of pain on anterolateral aspect of the shoulder for at least three months.
• At least 3 of the following criteria; positive Neer, Hawkins, and Empty can tests, Painful arc, and pain during resisted isometric abduction or external rotation.

Exclusion Criteria:

• Shoulder surgery, injury and arthritis.
• Any anatomical anomalies as hooked acromion.
• Cervical radiculopathy.
• Other systemic diseases: cardiovascular diseases, respiratory diseases and neurological diseases.