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Based on the scientific evidence in published literature about precipitation of musculoskeletal injuries in the workplace, four theories have been proposed to explain these afflictions. Central to all theories is the presupposition that all occupational musculoskeletal injuries are biomechanical in nature. Disruption of mechanical order of a biological system is dependent on the individual components and their mechanical properties. These common denominators will be causally affected by the individual's genetic endowment, morphological characteristics and psychosocial makeup, and by the occupational biomechanical hazards. This phenomenon is explained by the Multivariate Interaction Theory. Differential Fatigue Theory accounts for unbalanced and asymmetric occupational activities creating differential fatigue and thereby a kinetic and kinematic imbalance resulting in injury precipitation. Cumulative Load Theory suggests a threshold range of load and repetition product beyond which injury precipitates, as all material substances have a finite life. Finally, Overexertion Theory claims that exertion exceeding the tolerance limit precipitates occupational musculoskeletal injury. It is also suggested that while these theories may explain the immediate mechanism of precipitation of injuries, they all operate simultaneously and interact to modulate injuries to varying degrees in different cases.

Working postures are addressed in many papers in the ergonomics field but, surprisingly, scientific literature dealing with working posture itself is not common; knowledge has been elusive. This article reviews the working postures literature. Selected papers published in the English language before March 2003 including the phrase "working postures" in the title, abstract, or keywords were searched in the PubMed, Scirus, and Science Direct databases and reviewed. The literature provides evidence that working postures and musculoskeletal health are related. This relationship is supported by the overexertion, differential fatigue, and cumulative load theories of musculoskeletal injuries' precipitation. Goniometers, inclinometers, photographic techniques, electrogoniometers, and video recording systems are the means that are most often used to measure working postures. Information about working postures need to be collected and analyzed in a more systematic way in order to contribute for a deeper understanding of the relationship between working postures and work-related musculoskeletal disorders. This information will help to improve the control and rehabilitation of these highly prevalent disorders.

Muscle responses were greater with higher levels of acceleration. Because the muscular component of the head-neck complex plays a central role in the abatement of higher acceleration levels, it may be a primary site of injury in the whiplash phenomenon.

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Questionnaires were sent to 462 physical therapists in Edmonton, Canada, to determine the prevalence of work-related low back pain (LBP) and to characterize those who reported pain. Of the 311 (67.3%) valid questionnaires returned. 49.2% reported back pain due to work. The occurrence rates of work-related LBP among physical therapists in Edmonton was higher than that of the general population reported in Canada (27%), Great Britain (27%), and the United States (26-29%). There was no significant difference (p < or = 0.05) between those with and without work-related LBP. The initial onset of work-related LBP frequently occurred within the first 5 years of practice as a physical therapist, and before the age of 30. Hospitals and private practices were the most prevalent work settings in which injury occurred. Patient handling, bending, stooping, lifting, carrying, pushing, and pulling were the commonly described activities causing precipitation of injury. The severity of back discomfort had been sufficient to require 13.7% of therapists to stop their work. Despite LBP, 35.3% of the pain sufferers continued to work. Over half (55.4%) of the respondents with current work-related LBP demonstrated little or no disability.