NIOSH recently released the results of a study which found a correlation between the number of lifts per shift and lower back pain. The study involved the self-reporting of multiple factors from a group of 138 manufacturing workers. The workers spent their day lifting and assembling dryer parts.
The study used the NIOSH Lifting Equation to create a Composite Lifting Index (CLI) which provides an estimate of the stress undergone during lifting tasks. In the study, a CLI of >1.5 indicated a higher risk of self-reported lower back pain. The study found that lower back pain had the highest correlation (among the factors examined) to lifts per shift and to maximum lifting frequency. Workers experienced decreased lower back pain when they engaged in non-work activities, which involved bending and twisting, when they worked 10–19 weeks of overtime, and when they had been employed for 5–10 years overall (especially when compared with workers with <2 years of employment).
The researchers did indicate that these results were true for this specific population and other worker populations would need further study. The results for this population also need to be corroborated by other studies.
The results of the study are consistent with many of the beliefs about what causes low back pain, but — as noted — the constraints of the study make it difficult to draw clear conclusions across all employees who lift at work.
We expect there to be a link between lifting frequency and lower back pain. Repeated lifts every day at work will cause microtrauma, microtears in the muscle fibers and related tissues which can eventually contribute to a weakening of the musculoskeletal support system. Because pain due to microtrauma increases very slowly over time, workers may ignore and dismiss it until something major happens but would definitely notice an overall increase in lower back pain.
It’s not surprising that there is an increase in lower back pain among warehouse workers with only a few years of experience. Shorter-term workers may not yet be used to the wear and tear of the job, so they may experience more muscle soreness than those whose bodies have adjusted to the daily grind. Additionally, short-term workers are often subject to more stringent performance standards which would cause more frequent lifting and potentially less awareness of lifting form during a shift.
We’ll see if other studies find similar results among larger and more diverse working populations, and we are working to dive deeper into the effects of safe lifting form and frequency within these populations.
Products like Arc can help companies automate data capture of these repetitive movements that lead injuries. While job safety/hazard analysis is a primary tool to modify the workplace, it's also important to track data on a longitudinal scale to ensure the behaviors anticipated from the job safety analysis holds true.