What is the best method to relieve constant muscle pain/tightness under the shoulder blade curving to the side under my arms?

Muscular tension: Most of the causes of pain in the back of the chest is muscular in the setting of poor posture, scoliosis, osteoporosis or other. A kyphotic spine is one that bends forward. Stand up against a wall with your back of head resting against the wall. Your shoulder blades too should feel the wall.

Exercise: Muscle go into spasm for several reasons. An imbalance of chemistries: sodium, potassium, magnesium...Or dehydration are two possibilities. Most often, though, is a lack of active use: contracting and relaxing the muscles to coordinate them to work properly and maintain a natural state of muscle tone. Get started on a regular exercise ad strengthening program and eat more fruits and vegetables.

Danger here: Rule out danger first, like a pleural lesion on your lung. See your doc. It could also be a tendon tear , or muscle pain seen in patients who never sleep deeply. Relief depends on cause, a good diagnostician , see one.