Literature about muscle imbalances has graced exercise physiology textbooks for half a century. Athletic trainers, doctors, exercise physiologists and strength coaches have addressed and discussed musculature dysfunctions due to this idiom and it's causes at length.
Very little has ever been mentioned regarding imbalances of the jaw. There is a well- known relationship between the jaw, posture and one's ability to contract the arm muscles. Having a strong jaw and thick neck muscles has always been a sign of strength in humans. Throughout the 70's, study after study, showed strong correlations with bite force, jaw strength and the upper torsos ability transmit force.
Recently, scientists placed small spacers on one side of the mouth of a population of 20 normal healthy men and women. They found if the jaw was imbalanced the contralateral arm, that is the arm on the opposite side of the spacer, became weaker.
If you train the head and neck muscles an athlete's shoulder strength will improve. If an athlete injures the muscles around the head, neck or jaw make sure you rehab this area. Shoulder weakness post head injury, in some cases, may show up on the opposite side of the trauma until rehabilitated.
Pendulum Head and Neck Machines Get you Strong