Like Lower Cross Syndrome, Upper crossed syndrome (UCS) affects the muscles in the neck, shoulders, and chest. It typically occurs due to the nature and result of poor posture. The muscles that are typically the most affected are the upper trapezius and the levator scapula, which are the back muscles of the shoulders and neck. These muscles typically become very short and tight along with the chest muscles (i.e. pectoralis). Conversely, the muscles that become weak are the deep neck flexors and the lower trapezius.