[Electromyogram measuring method for low back load evaluation of handling weight and forward bending posture]

In order to establish a measuring method of electromyogram (EMG) to evaluate the low back load by handling weight and forward bending angle. EMG at Th5-6, Th8-9, Th11-12, L1-2 and L3-4 were measured in ten male subjects. The handling weight was changed at 0, 10, 20 and 30 kg, and the forward bending angle was changed at 0, 30, 60 and 90 degree. The following results were obtained: 1) EMG increased according to the handling weight at all forward bending angles. The increasing rate of EMG at Th5-6 was larger than that at L1-2 or L3-4. Thus, EMG at higher position such as Th5-6 was found to be appropriate to evaluate handling weight-load. 2) The effect of forward bending angle was different by handling weight. EMG at L1-2 and L3-4 increased according to forward bending angle when the handling weight was 0 kg or 10 kg and when the forward bending angle was not greater than 60 degree. However, when the handling weight was 20 kg or 30 kg, EMG and forward bending angle did not show a simple proportional relationship. Thus, EMG at L1-2 or L3-4 could be used to evaluate posture load when the handling weight was light and the bending angle was not so large. However, it was difficult to use EMG to evaluate posture load when the forward bending angle was large or the handling weight was heavy.