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|Classification and external resources|
|Classification and external resources|
Musculoskeletal disorders (MSDs) are injuries or pain in the body's joints, ligaments, muscles, nerves, tendons, and structures that support limbs, neck and back. MSDs are degenerative diseases and inflammatory conditions that cause pain and impair normal activities. They can affect many different parts of the body including upper and lower back, neck, shoulders and extremities (arms, legs, feet, and hands). MSDs can arise from a sudden exertion (e.g., lifting a heavy object), or they can arise from making the same motions repeatedly repetitive strain, or from repeated exposure to force, vibration, or awkward posture. Examples of specific MSD disorders are carpal tunnel syndrome, epicondylitis, and tendinitis. Abrasions, contusions, and fractures that occur from sudden physical contact with objects that might occur in an accident are not considered MSDs.
Since MSDs involve soft tissue, there are often no visible signs of injury. Therefore, assessments are based on self-reports by people as to whether or not they are experiencing pain. A popular measure of MSDs is the Nordic Questionnaire that has a picture of the body with various areas labeled and asks the individual to indicate in which areas they have experienced pain, and in which areas has the pain interfered with normal activity
MSDs can arise from the interaction of physical factors with economic, psychological, and social factors.
MSDs are caused by biomechanical load which is the force that must be applied to do tasks, the duration of the force applied, and the frequency with which tasks are performed. Activities involving heavy loads can result in acute injury, but most occupation-related MSDs are from motions that are repetitive, or from maintaining a static position. Even activities that do not require a lot of force can result in muscle damage if the activity is repeated often enough at short intervals. MSD risk factors involve doing tasks with heavy force, repetition, or maintaining a nonneutral posture. Of particular concern is the combination of heavy load with repetition. Although awkward posture is often blamed for lower back pain, a systematic review of the literature failed to find a consistent connection.
People vary in their tendency to get MSDs. Gender is a factor with a higher rate in women than men. Obesity is also a factor, with overweight individuals having a higher risk of some MSDs, specifically lower back.
There is a growing consensus that psychosocial factors are another cause of some MSDs. Some theories for this causal relationship found by many researchers include increased muscle tension, increased blood and fluid pressure, reduction of growth functions, pain sensitivity reduction, pupil dilation, body remaining at heightened state of sensitivity. Although research findings are inconsistent at this stage, some of the workplace stressors found to be associated with MSDs in the workplace include high job demands, low social support, and overall job strain. Researchers have consistently identified causal relationships between job dissatisfaction and MSDs. For example, improving job satisfaction can reduce 17-69 per cent of work-related back disorders and improving job control can reduce 37-84 per cent of work-related wrist disorders 
Any activity that involves repeated biomechanical load can contribute to MSDs. Such conditions are frequent in the workplace, but can occur in the home or leisure activities. For example, parents are at risk for MSDs due to lifting and carrying young children. Participation in sports can lead to MSDs, and is a leading cause of ankle injuries.
The target of MSD prevention efforts is often the workplace in order to identify incidence rates of both disorders and exposure to unsafe conditions. Groups who are at particular risk can be identified, and modifications to the physical and psychosocial environment can be made. Approaches to prevention in workplace settings include matching the person's physical abilities to the tasks, increasing the person's capabilities, changing how tasks are performed, or changing the tasks.
Encouraging the use of ergonomics not only includes matching the physical ability of the worker with the correct job, but it deals with designing equipment that is correct for the task.  Limiting heavy lifting, training, and reporting early signs of injury are examples that can prevent MSD.  Employers can provide support for employees in order to prevent MSD in the workplace by involving the employees in planning, assessing, and developing standards of procedures that will support ergonomics and prevent injury. 
MSDs are an increasing healthcare issue globally, being the second leading cause of disability. For example, in the U.S. there were more than 16 million strains and sprains treated in 2004, and the total cost for treating MSDs is estimated to be more than $125 billion per year. In 2006 approximately 14.3% of the Canadian population was living with a disability, with nearly half due to MSDs. Neck pain is one of the most common complaints, with about one fifth of adults worldwide reporting pain annually.
Most workplace MSD episodes involve multiple parts of the body. MSDs are the most frequent health complaint by European, United States and Asian Pacific workers. and the third leading reason for disability and early retirement in the U.S. MSDs are widespread in many occupations, including those with heavy biomechanical load like construction and factory work, and those with lighter loads like office work. The frequency of injury and body parts affected vary by occupation. For example, a national survey of U.S. nurses found that 38% reported an MSD in the prior year, mainly lower back injury.