The effects of load knowledge on stresses at the lower back during lifting

This study investigated the effects of load uncertainty on the lifting characteristics of 40 male volunteers during the initial portion of a lift. Twenty subjects were experienced weightlifters while another 20 were subjects who had never lifted weights nor held a job that required them to on a regular basis. The subjects each lifted a container 20 × 45 × 40 cm, with handles, from floor to waist height 12 times with loads of 68, 10·2 or 13·6 kg. The loads were lifted under conditions of either havingor not having verbal and visual knowledge of the load magnitude prior to the lift. The subjects were allowed to perform the lift in a manner of their choosing. A 2 (groups) × 3 (loads) × 2 (load knowledge) ANOVA was performed on the data. Maximim force (F_max) value analysis revealed group and technique differences. The experienced lifters had lower stress levels at L4/L5 and utilized two technique strategies that were dependent upon the load knowledge condition, whereas the non-lifters used the same strategy for all lifts. Maximum moment values (M_max were significantly higher for the inexperienced lifters under all conditions, indicating a greater dependence on the low back musculature for initiating the lifting of a load.