Manual material handling (MMH) involves considerable physical work demands and is considered a high-risk task for low back pain (LBP). The risk increases with the magnitude of the physical exposure in terms of the load moment, trunk motion dynamics and trunk posture. There exists a large variability in low back loading and lifting posture that could be explained by individual differences (between subjects) and by trial-to-trial variations. Thus, for the same task, spine loading and posture can change markedly between trials and individuals.

The above study showed that 'expert' workers differed from novices mostly in the posture-related variables (lumbar flexion angle, trunk inclination, knee flexion) and much less in the back loading ones (peak resultant moment or asymmetrical moment at L5/S1). Experts posture was quite different from the novices at the instant of the peak resultant moment as they bent their trunk and lumbar region less (even when age was accounted for with the lumbar flexibility index). Moreover, their knees were more flexed when the box was lifted from the floor of the pallet. Experts were also closer to the box during both the lifting and the deposit phases (See Image).

These posture-related variables could have a major impact on the distribution of internal forces on the spine, but expertise had a very small effect on the external back loading variables (peak resultant moment and peak asymmetrical moment at L5/S1), which are important indicators of risk in terms of work-related back injuries.

Various intervention strategies, such as training employees in safe lifting techniques, are used with the aim of protecting workers from back injuries. Recent reviews have seriously questioned the effectiveness of training programs as a mean of reducing back injuries. However, these reviews are based on a small number of studies, and the quality of the training intervention is generally not questioned. Important aspects such as the content of the training course, its duration and its specificity to the work context are worth consideration. 

A simple question that still needs to be answered is  “What should be taught?”.

Manual handling training is generally given over a very short time; as a result, the “training” is really more of an information session. When training is specific to the task and dispensed over a longer timeframe, a decrease in back loading and back injuries is possible (Schibye et al., 2003). The following study suggests ergonomic intervention with the aim of reducing external back loading should primarily focus on major factors such as the load height and horizontal distance between the lumbar spine and the load lifted in order to reduce the external back moment, and not just on workers’ technique.