Summary

Many women work as material handlers, yet there has been little interest in this population because most material handlers are men. Some studies have noted significant differences in how men and women perform handling tasks, but such studies are few and far between. Nonetheless, though there are far fewer women handlers in certain sectors (transport and equipment operation, for example), in others, such as food and services, women often constitute close to half the labour force and must occasionally perform material handling tasks. It is thus important to study this population. The purpose of this research project was to gain a better understanding of the differences in how women and men handlers work. It was assumed that the work strategies of experienced women material handlers would differ from those of male handlers.

The data from this study were compared with those gathered for a study comparing expert and novice male workers (Plamondon et al., 2010). The study was designed to highlight the differences between men and women in a work context where the load was the same in absolute terms (15 kg for both sexes) or in relative terms (men: 15 kg; women: 10 kg)—given that a woman’s strength is, on average, approximately two-thirds that of a man (10/15 kg = 2/3). Three experimental sessions were held. The first consisted mainly in evaluating the physical capacities of the subjects and giving them a chance to become familiar with the experimental conditions. In the two other sessions, the handlers performed tasks in two different contexts. Load characteristics (weight, fragility and centre-of-gravity offset), lifting and deposit height and handler fatigue were modified to solicit the widest possible variety of work techniques from the handlers.

Biomechanical data were gathered and ergonomic observations were made during the three experimental sessions using motion tracking systems, a large force platform and a system for measuring muscle activation. The results demonstrate that the women handlers in our study (15 subjects) are not as strong as the expert male handlers (15 subjects) or the novice male handlers (15 subjects), with muscle strength (lifting strength and trunk muscle strength) measuring between 49% and 63% of that of the men. Given the size differences of the sexes, it was also expected that peak loading of the back (resultant moment at L5/S1) during the handling tasks would be higher in the men. However, when the resultant moments were normalized with trunk weight, these differences disappeared in most cases. On the other hand, the results show that the women worked differently from the expert male handlers, using techniques more like those employed by the novice male handlers. For the same absolute load of 15 kg, for example, the women, compared to the expert male handlers, took longer to transfer the boxes; inclined the upper body more; bent the lower back more; bent the knees less when lifting boxes from the floor; had lower trunk angular velocity; and kept the boxes closer to their bodies. Most of the women used a very different lifting technique from the expert male handlers, which basically involved extending the knees first and the upper body after. This technique can cause greater lumbar flexion than is observed in expert male handlers and can place the internal passive structures of the lumbar spine at risk. On the other hand, it is a very efficient technique energywise.
When the same relative load was handled (men: 15 kg; women: 10 kg), both back loading and task duration diminished for the women. However, the women held the boxes farther from their bodies with the smaller load, and so lumbar flexion did not decrease under most conditions. This means that the most direct method of intervention is to reduce the load carried by the women, but this will not reduce lumbar flexion under most conditions. Training is another type of intervention, but it has little impact on lumbar loading. A third possibility is to increase the height from which the boxes are lifted. In fact, most of the risks reported herein apply only under handling conditions where the load is lifted from the floor—a fraction of most handling tasks. The risk to the back drops substantially when the load is lifted from hip height. All these types of intervention not only increase the safety margin for the back but also reduce the physical exposure of handlers, men as well as women.