Kyphosis affects the muscles of the upper back and neck. Kyphosis is defined by MedlinePlus as a back deformity that produces rounding of the shoulders and a slouching or hunchbacked appearance.
The disorder may be caused by spinal problems such as fractures and trauma to the vertebrae, but the issue could be due to posture and muscle imbalances. For example, Sportsinjuryclinic.net claims that baseball pitchers are very prone to this disorder as they are forced to hold a particular posture while standing on the pitching mound. Amateur bodybuilders who overdevelop their chest muscles to the expense of their upper back are also at risk. When the disorder is due to muscular imbalances, it is called upper cross syndrome because strong muscle groups are connected to weak muscle groups in a cross shape from the front to the back of the spine. The trapezius, latissimus dorsi, sternocleidomastoid and rhomboids in particular are weak and short with this syndrome.