5

Design of repetitive tasks

Doctors can only diagnose diseases that they know…This is why new diseases, after their first description, are seen everywhere - Aids, for example. If the physician is unaware that a certain constellation of symptoms and signs indicates a particular disease, there is no possibility of a diagnosis being reached. (Skrabanek and McCormick, 1990)

Most repetitive tasks require a combination of both static and rhythmic muscle activity. In manual work, postural stabilisation of the hands and arms is essential for carrying out all but the grossest movements in a purposeful way. This stabilisation is provided by muscles farther up the kinetic chain, muscles that cross the elbow and shoulder joints and have their origins in the cervical spine and thoracic regions. If task demands are excessive, pain may be experienced in the muscles providing the stabilisation or in the muscles and joints of the effectors, or in both. Over time, a medical condition may develop.


Introduction to work-related musculoskeletal disorders

The relationship between task demands, ergonomics and musculoskeletal disorders is of a probabilistic nature and is confounded by the fact the disorders can arise as a result of many activities of daily life, both at work and elsewhere. The disorders may present as co-conditions of other diseases. Disorders such as cervical spondylosis, carpal tunnel syndrome and tennis elbow are very common, particularly in older people. The usual pattern is for symptoms to appear before objective signs of degeneration or disease. By the age of 50 years, 50% of studied populations have had neck, shoulder or arm pain (Lawrence, 1969). This number increases steadily with advancing age.

There appear to be two main camps in the debate about the work-relatedness of musculoskeletal disorders. There are those who believe that if a person experiences pain at work it must be the work that caused it and that the pain itself is evidence of an underlying medical condition, caused by the work. People in this camp draw little distinction between the words 'pain', 'disorder' and 'injury' and use terms such as RSI (repetitive strain injury) and CTD (cumulative trauma disorder) as collective nouns to describe any kind of musculoskeletal problem, irrespective of whether it falls into a medical diagnostic category or not. Those in the second camp believe that there is a lack of evidence that work causes musculoskeletal diseases, apart from

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