Accuracy of visual estimation in classifying effort during a lifting task.

OBJECTIVE The objective was to determine if visual estimation of effort (VEE) during lifting tasks is accurate in classifying relative levels of exertion or distinguishing between incomplete lifts that may be potentially unsafe and incomplete lifts of "actors" feigning weakness. PARTICIPANTS A convenience sample of 117 health professionals and lay subjects participated in the study. METHODS Four actors were videoed performing four complete dynamic lifts (sets of five repetitions) of varying levels of exertion (relative to subjects' physical maximum). Subjects viewed the videoed performances, presented in no apparent order, attempting to properly classify the lifting tasks. For the four levels of exertion, participants were to judge if the lifts were 25%, 50%, 75% and 100% of each actor's maximum lifting capacity and to distinguish between an incomplete (failed) lift of 110% of maximum and a feigned failure of a lift of 25% of maximum. RESULTS Accuracy for in classifying all lifting activities was marginally higher than chance. There were no differences in the accuracy of health professionals or lay subjects. CONCLUSION The VEE does not accurately classify relative levels of exertion or distinguish between incomplete feigned effort lifts and lifts that are potentially too heavy to safely lift.