Force Exertion during Lifting with Light Loads

Abstract

A single male subject lifted a tote box 12 times at each of 24 conditions while standing on a force platform. The 24 conditions were 6 combinations of initial and final position (floor to 12,24 and 36 in. shelf, floor plus 12 in. to 24 and 36 in. shelf, and floor plus 24 in. to 36 in. shelf) x 2 box weights (11 and 22 lbs.) and 2 distances of the box from the body center of gravity (16 and 20 in.).

Averaged over all 24 conditions, peak vertical force was 46 lbs., frontal force was 6 lbs., lateral force was 2 lbs., somersault torque was 417 in.-lbs., cartwheel torque was 75 in.-lbs., twist torque was 59 in.-lbs. and peak box acceleration was .3 g.

For lifting with light loads, object weight has much less effect on stress than might be expected. Peak forces occurred in the .5 sec. before and after grasping the box. In fact, peak stress occurred before the box was grasped in 66% of the lifts.