Summary
This study indicates that heavy work provokes a facet joint syndrome as a cause of low back pain. However it also shows that heavy work may well strengthen the back and actually protect against a different type of back pain due to accidental back strain.
Heaviness of work did not seem to cause back pain due to inflammatory pelvi-spondylitis nor nerve root compression due to prolapsed intervertebral disc. If the effects of heavy work had solely been examined on an overall grouping of back pain patients, little would have been evident as the effects would have cancelled out for the facet joint and back strain syndromes and those patterns showing no relationship to heaviness would have diluted out any remaining evidence.
These findings depended on the ability to distinguish different types of common low back pain.