Worker health Musculoskeletal disorders include a group of conditions that involve the nerves, tendons, muscles, and supporting structures such as intervertebral discs. They represent a wide range of disorders, which can differ in severity from mild periodic symptoms to severe chronic and debilitating conditions. Musculoskeletal disorders affect 7% of the population and account for 14% of physician visits and 19% of hospital stays (source: National Institute for Occupational Safety and Health, 1997).