Studies were made of two different techniques of bi-manual lifting with bent legs (A and B) and a technique of lifting with the back bent and the knees almost extended (C). With technique A, the trunk was almost vertical, while with B it was erect and more forward inclined and the heel of the front foot kept in contact with the support. Two healthy subject samples (n = 18 and n = 16 respectively) were studied, both employing a force platform; with the second sample the back muscles were also evaluated by electromyography.
The distance A L between the lines of gravity of the body and the load at the start of the lifts was shortest with technique A and longest with C. This was true whether the position of the feet was chosen spontaneously or was identical for all three techniques. The distance of the load from the body during the lifting movement was directly related to the distance at the start of the lift: the further away the load was at initiation of the lift, the further away it remained throughout the rest of the lift. A request to lift as close to the load as possible had a positive effect in shortening A L, but the amount of previously received instruction in lifting technique did not correlate with the spontaneously chosen A L.