Even if you don’t sit at a desk all day, activities like driving, watching TV, looking down at your computer or phone, or even exercising your muscles unevenly (i.e. doing too many chest presses and not enough rows) can cause your shoulders to get tight.

The issues don’t stop there. Sitting all day can also put pressure on our SITS muscles – the Supraspinatus, Infraspinatus, Teres Minor, and Subscapularis. These rotator cuff muscles support and stabilize our complex shoulder joint. When we are hunched over, the rotator cuff muscles and the pecs can stiffen, leading to tightness, pain, and loss of mobility in the arms and neck.

via paleohacks.com