The shoulder joint is reliant on soft tissues working well together.
Here's the knee joint (side view) bending and straightening. (X-Ray GIFs)
Forward Head and Neck Forward head posture and shoulders rounded forward are common signs of this set of muscle imbalances. For every inch your head moves forward out of alignment from your shoulders, your neck effectively carries an additional ten pounds of weight. Forward head and neck postural dysfunction is a frequent cause of neck and upper back pain, not to mention headaches, shoulder pain and more. - See more at…
Text Neck Syndrome, Not Just a Neck Problem. Chiropractic, Massage, Physical Therapy.
Fix the Posture: Are we so beaten down by life, we have to stand that way too?
For every inch that the head moves forward in posture, it increases the weight of the head on the neck by 10 pounds, which greatly increases the likelihood of head and shoulder tension, pain, and injury. Try to stand and sit up straight. :)
Trigger Point Pain Zones in Low Back Pain Complaints