Forward Head and Neck Muscle Imbalance. 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. Tight muscles: Anterior deltoid Pectoralis Latissimus dorsi Weak muscles: Middle trapezius Lower trapezius Infraspinatus Teres minor