QUALITATIVELY DIFFERENT MODES OF MANUAL LIFTING

The question of whether qualitatively different modes of manual liftin g exist is addressed via an ideographic analysis of data from an exper iment in which 39 subjects lifted loads of varying mass. Angular motio n in the sagittal plane of ankle, knee, hip, and lumbar vertebral join ts was estimated from video images collected while each subject perfor med 100 lifts. Bimodality in the frequency distribution of postures ad opted at the start of lifting was evident in the data from 4 subjects. While semi-squat postures were usually adopted at the start of liftin g, on some trials a stooped posture was observed. The likelihood of a stooped posture being adopted at the start of lifting was related to l oad mass. Both postures were observed when the load mass was relativel y light, while only the semi-squat posture was observed when the load mass was increased. Subjects who adopted stooped postures on some or a ll trials were also, on average, taller, heavier, and stronger.