OBJECTIVETo evaluate the work load and related factors for asymmetric lifting tasks using surface electromyography (EMG).

METHODSThirteen male volunteers lifted loads of 6 and 13 kg at two speeds, in varying angles of trunk rotation, from floor to knuckle height, performing 16 lifting tasks. During lifting, surface electromyography signals from the erector spinae, bilaterally at level of T10 and L3, was continually recorded. The work load and related factors for asymmetric lifting tasks were evaluated by comparing the average amplitude of EMG signals.

RESULTSThe EMG average amplitude when lifting the load of 13 kg (43.30% MVE) was significantly greater than that when lifting the load of 6 kg (37.70% MVE) (P < 0.01). The EMG average amplitude when lifting at the higher speed (41.80% MVE) was significantly greater than that at the lower speed (39.19% MVE) (P < 0.05). The EMG average amplitude was increased with the increase of the trunk rotation angle without significant difference (P > 0.05). At T10, the EMG average amplitude was greater on the right side than that on the left side (50.31% MVE and 25.88% MVE respectively) while at L3, it was on the contrary (45.60% MVE on the left and 40.22% MVE on the right respectively) (P < 0.01). Multiple stepwise regression analysis showed that the load of lifting was the factor contributing most to the EMG average amplitude followed by the lifting speed.

CONCLUSIONThe risk factors related to work load for asymmetric lifting tasks are mainly the load and the speed of lifting. The EMG activity between the right and left side of erector spinae is different during such lifting.