THE MUSCULAR LOAD ON THE LOWER BACK AND SHOULDERS DUE TO LIFTING AT DIFFERENT LIFTING HEIGHTS AND FREQUENCIES

The aim of the study was to investigate the muscular load on the lower back and shoulders and the circulatory load on employees at a post ce nter during repetitive lifting of mail transport boxes. A mock-up was designed in the laboratory, a total of nine combinations of lifting he ight and frequency were studied. Surface EMG was recorded bisymmetrica lly from m. erector spinae (L3-level) and m. trapezius. The circulator y load was evaluated by measuring the heart rate. The results show a t rade off between the low back and shoulders. The maximum load on the l ow back occurred at the low lifting height (36.3 and 54.4 cm) whereas the maximum load on the shoulders occurred at the high lifting height (144.9 and 163.0 cm). (C) 1998 Elsevier Science Ltd. All rights reserv ed.