My brother-in-law and I have an ongoing debate we’d like you to settle. He’s a postal worker and I’m a firefighter. He maintains that pushing and pulling heavy carts full of mail is just as likely to cause back injuries as hauling heavy hoses and pushing ladders around. We both know plenty of people in our respective work places to suffer back injuries from these activities. But I still think firefighters are under much more physical stress than postal workers. What do you think?

Many researchers, physicians, and workers have asked: what causes low back pain at work? Is it the lifting? The pushing? The pulling? Researchers from Canada have published a report on the 2,766 studies they found on low back pain in the work setting.

Type of occupational setting included various levels of manual labor. There were firefighters, nurses, salespersons, kitchen helpers, postal workers, shipbuilders, physicians, and steel mill workers, to name a few.

In theory, it makes sense that shearing forces are applied to the spine during pushing and pulling activities. Load and compression on the intervertebral discs occur. But are these forces enough to cause overload injuries to the low back area?

In this case of looking at the effect of physical activity (pushing/pulling) on low back pain, it would be helpful if the task measured by each study was described quantitatively (how much load, how often, direction, duration).

And these factors should be examined in light of when and how the low back pain occurs. The result would be a measure called dose response (i.e., what type of load is linked with low back injury).

But in the studies published so far, this type of information wasn’t gathered. And many of the studies were retrospective (after the fact). The results are subject to a phenomenon called recall bias — failure to remember accurately.

So at this point, there just isn’t enough evidence to say that pushing/pulling activities on-the-job causes low back pain. Nurses pushing and pulling heavy hospital beds do suffer low back pain. But whether it was the pushing/pulling activity or something else remains unproven. Likewise for any of the other workers (postal versus firefighters) engaged in occupations studied.

There is a need for high-quality studies using a prospective cohort design. Prospective cohort means the workers are studied on an ongoing basis rather than asked after they have suffered a back injury what factors were involved.

This type of design helps eliminates recall bias. Statistics gathered as the injuries occur are more accurate in detail (how, what, when) compared with asking workers weeks to months later what happened and how it happened.