WEIGHT AND FREQUENCY EFFECT ON SPINAL LOADING IN A BRICKLAYING TASK

In manual materials handling jobs a reduction in the weight of materia ls often concurs with an increase in handling frequency. The effect of weight and inversely related frequency on spinal load was studied in two bricklaying tasks: building the skin and the floor of a steel ladl e. In both tasks five subjects laid bricks of varying weight and frequ ency (obtained from held observations). The load parameters investigat ed were peak values and time integrals of the compressive force on the L5-S1 motion segment and stature loss, which is assumed to reflect mo tion segment creep due to compression. Peak compression was found to i ncrease at higher brick weights. No differences in integrated compress ion were observed among four out of five combinations of weight and fr equency (both in skin and floor building). Laying bricks for a fixed p eriod of 47 min yielded average stature losses of 2.0-3.6 mm. Differen ces in stature loss among weight-frequency conditions were not signifi cant. In conclusion, at lower weights peak loads decrease, but the ben efit of this should be doubted because the frequency of exposure to th ese peak loads was found to increase. Moreover, this increase was such that no effects were found on spinal load estimates that incorporate both magnitude and time aspects of the load, like time-integrated comp ression and stature loss. Copyright (C) 1996 Elsevier Science Ltd.