Working height, block mass and one- vs. two-handed block handling: the contribution to low back and shoulder loading during masonry work.

The goal of this study was to compare the effects of the task variables block mass, working height and one- vs. two-handed block handling on low back and shoulder loading during masonry work. In a mock-up of a masonry work site, nine masonry workers performed one- and two-handed block-lifting and block-placing tasks at varying heights (ranging from floor to shoulder level) with blocks of varying mass (ranging from 6 to 16 kg). Kinematics and ground reaction forces were measured and used in a 3-D linked segment model to calculate low back and shoulder loading. Increasing lifting height appeared to be the most effective way to reduce low back loading. However, working at shoulder level resulted in relatively high shoulder loading. Therefore, it was recommended to organise masonry work in such a way that blocks are handled with the hands at about iliac crest height as much as possible.