Individual risk factors
Although results of epidemiological studies are not necessarily consistent, factors that have been reported to be associated with low back pain are age, physical fitness, and strength of back and abdominal muscles. There seems to be no association between low back pain and other individual factors such as gender, length, weight, Body Mass Index, flexibility/mobility and structural deformities of the spine.
Recent systematic reviews found that smoking and body weight should be considered weak risk indicators and not causes of low back pain [13, 14], and
Table 7.1 Risk factors for occurrence and chronicity
Strength of back and abdominal muscles
Mood/emotions Cognitive functioning Pain behavior
Manual material handling Bending and twisting Whole-body vibration Job dissatisfaction Monotonous tasks Work relations/social support Control
Low educational level
High levels of pain and disability
Depressive mood Somatization
Unavailability of light duties on return to work Job requirement of lifting for % of the day that alcohol consumption , standing or walking, sitting, sports, and total leisure-time physical activity  do not seem to be associated with low back pain.
Psychosocial factors that traditionally have been reported to be associated with low back pain are anxiety, depression, emotional instability, and alcohol or drug abuse . A recent systematic review of observational studies of psychosocial factors for the occurrence of back pain found insufficient evidence for an effect of psychosocial factors in private life, such as family support, presence of a close friend or neighbor, social contact, social participation, instrumental support and emotional support .
A prospective cohort study provided evidence that psychologic distress at 23 years of age more than doubled the risk of low back pain onset 10 years later, while other factors (e.g. social class, childhood emotional status, Body Mass Index, job satisfaction) did not increase the risk . Another systematic review found a clear link between psychologic variables and low back pain . Psychologic variables that are associated with low back pain are stress, distress or anxiety as well as mood and emotions, cognitive functioning, and pain behavior.
Occupational factors such as physically heavy work, lifting, bending, twisting, pulling and pushing (or the combination of these last three with lifting), and vibrations have often been associated with low back pain .
A systematic review of aspects of physical load found strong evidence that manual materials handling, bending and twisting, and whole-body vibration are risk factors for back pain . Two systematic reviews of psychologic workplace variables in back pain found strong evidence that job dissatisfaction, monotonous tasks, work relations, social support in the workplace, demands, stress, and perceived ability to work were associated with the occurrence of low back pain [17, 21]. Moderate evidence was found for work pace, control, emotional effort at work, and the belief that work is dangerous, and insufficient evidence was found for a high work pace, high qualitative demands , low job content and low job control .
Studies on the association between occupational risk factors and low back pain are hampered by the difficulties of measuring exposure to specific factors. Exposure to specific risk factors may vary among employees with the same job, but also the task they perform may vary. Also, the "healthy worker effect" may considerably affect results of epidemiologic studies in occupational settings. That is, healthy workers may stay on the same job or perform the same task for years, while workers with low back pain may have moved to another job or function or their tasks may have been adjusted.
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