Apply Pressure along the rotator cuff tendons (depicted in blue). Pain/Soreness due to pressure is a sign of inflammation of tendons attributed to rotator cuff stress/injury.

See Below for specific injuries:

The Supraspinatus muscle runs along the top of the shoulder blade. Do you have difficulty/pain when lifting your arm away from your body?

Symptoms of injury include: top of shoulder tenderness, sharp pain down arm, weakness of arm, problems lifting, reaching, arthritis, increased upper back and neck injuries, frozen shoulder.

The Infraspinatus a key muscle involved in stabilization of shoulders and movements that require turning the arm outward. Do you have trouble reaching behind your back?

Symptoms of Infraspinatus Injury: pain at the back of the shoulder, difficulty and discomfort during external rotation of the arm, and weakness in the arm, particularly when trying to rotate the arm outward or reach behind the body.

The Teres Minor assists in the external rotation of the arm and contributes to overall shoulder stability. Is your back muscle contantly injured?

Symptoms associated with Teres Minor injuries: pain or discomfort in the outer shoulder, particularly with movements that involve rotating the arm away from the body, and a general feeling of weakness in the external rotation of the shoulder.

The Subscapularis is responsible for medially rotating the arm, pulling strength toward the body, and stabilizing the shoulder. Do you feel sharp pains in shoulder/back/arms?

Symptoms of Subscapularis injury: pain at the front of the shoulder, difficulty in internal rotation movements (like reaching the back or tucking the shirt in), a sensation of weakness in the arm when attempting to rotate it inward or lift it, and potentially a feeling of the shoulder 'giving way' during certain activities.