You may be referring to a recent systematic review from the Ottawa Hospital Research Institute. A group of epidemiologists (people who study statistics and trends) did a literature review of all published studies on pushing and pulling as possible causes of low back pain.
They used well-known search engines (e.g., Medline, CINAHL, EMBASE) to look for any studies published between 1966 and as late as 2007 on this topic. They found 2,766 citation but after reviewing them all, there were only 13 studies that could be included.
In order for the information gathered to have validity, there had to be at least 30 people in each study. Workers with low back pain or injury was the target group so anyone with neck pain, whole spine pain, or on sick leave for other reasons was not included. Pushing and pulling were the only risk factors studied. Workers exposed to vibration, environmental factors, or psychosocial issues were not included.
When it was all said-and-done, it wasn’t that there was no link between pushing/pulling and low back pain. There just wasn’t enough evidence to prove the two are related. Of the 13 studies included, only eight were high enough quality to be taken seriously.
And even with the data combined from those eight studies, the statistical evidence to support pushing/pulling work activities as the cause of low back pain just wasn’t there. More studies of high-quality are needed in this area before firm conclusions can be drawn.