Abstract
The purpose of this study was to investigate the effects of load uncertainty on the lifting characteristics of the subjects. Forty male subjects volunteered for this study. Twenty subjects were members of the Texas A&M Powerlifters Club who had been lifting a minimum of five days per week, two hours per day, for at least one year. Twenty subjects were individuals who had never lifted weights nor held a job that required such on a regular basis. The subjects each performed 12 lifts from floor to waist height with a 20 (depth) x 45 (height) x 40 (width) cm container with handles. Loads of 6.8, 10.2, and 13.6 kg (15, 22.5, and 30 lb.) were lifted under conditions of either having knowledge of the load magnitude (both verbal and visual) or not having such knowledge prior to the lift. The subjects were allowed to perform the lift in any manner they deemed appropriate. A 2 (groups) x 3 (loads) x 2 (load uncertainty) ANOVA was performed on the data. The analysis of initial trunk position revealed an interaction among all three variables examined. The trunk angle increased from the horizontal with load under knowledge of load conditions, and was highest for the condition in which the subjects had no knowledge of the load, with non-lifters evidencing lower initial angles. Analysis of pull duration found a load x load certainty interaction which indicated that the 6.8 kg (15 lb.) load in the knowledge of load condition had the shortest duration while the 13.6 kg (30 lb.) load in the no knowledge of load condition had the longest duration. Irregular transient periods occurred more often in the non-lifters, indicating an attempt to correct unrealistic load expectations during the early portions of the lift. The lifters utilized two strategies which were dependent upon the load knowledge condition. Maximum bone-on-bone force (Fmax) value analysis revealed group differences, with the non-lifters having higher stress levels at the L4/L5 segment. This was traced to the use of lower trunk positions and use of alternating muscle groups to provide movement corrections. Maximum moment values (Mmax) were significantly higher for the non-lifters and were found to reflect trunk position and dependence on the extensor muscles of the trunk to perform a movement.
Patterson, Patrick Edwar (1984). The effects of load uncertainty on stresses at the lower back during the pull phase of light load lifting by experienced and non-experienced lifters. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -411124.