Low back stress, muscle usage, and the appearance of transient load movement during manual lifting

Neuromuscular involvement should be considered in biomechanical evaluations of a worker's job-related stresses as a potential aid to understanding and reducing the rising incidence of low back problems in industry. Because such interactions have seldom been investigated in multisegmental movements, the present study was undertaken to determine the effects of the involvement of the neuromuscular system during lifting by creating conditions in which subjects had prior knowledge (PK) of a load's magnitude as well as when they had no prior knowledge (NK). Two groups of subjects, experienced and inexperienced lifters (N=40), lifted loads varying from 6.8 to 13.6 kg under both the PK and NK conditions. Results indicated that two general patterns of load movement were used by the subjects: smooth and oscillatory (irregular transient), with higher peak L4/L5 forces and higher peak trunk movements found in the oscillatory pattern. Significant differences on all stress values were demonstrated by the inexperienced lifters. The inclusion of lift preparation and load knowledge considerations in training programmes and biomechanical models is recommended.