The pectoralis major and pectoralis minor influence your posture. The pectoralis major is attached to your clavicle, sternum and the cartilage of your 1st through the 6th rib. It attaches to the greater tubercle of the humerus. The pectoralis major action is to adduct the shoulder, medially rotate, flex the shoulder, horizontally adduct the shoulder and extend the shoulder. What does all that mean in plain language? It moves your arm at the shoulder joint.
The pectoralis minor is attached to the 3rd, 4th and 5th ribs. It attaches to the coracoid process of the scapula (it is under the pec major). The pectoralis minor action is to depress the scapula, abduct the scapula and downwardly rotate the scapula (rounds the shoulders forward).
When you sit at your desk or in your car for long periods of time those pecs are in constant use and in a shortened position. When you have a muscle in a shortened period for long periods of time it holds that shortened position (it gets tight). The opposing muscles are getting stretched, locked long and weakened. This is why you feel pain in the upper back and neck. The muscles of the upper back want to go back to their natural position.
What can you do to fix this? You might want to get a new job where you don’t have to sit at a desk. Will that really happen? Not likely. So how can you be proactive?
Make sure your desk is set up ergonomically.
Take frequent breaks from your desk.
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