年齢による筋力低下と身長が荷物持ち上げ時の腰部椎間板圧縮力に与える影響

抄録

Observational methods such as NIOSH lifting equation (NLE) are used for risk assessment of low back pain. The observational methods can easily assess the risk of low back pain, whereas they hardly consider the individual differences such as age and height. The aim of this study was to investigate the effect of age and height on L5/S1 compression force during manual material handling. The L5/S1 compression force was estimated by digital human modeling (DHM) simulation. The simulation conditions were the gender (male and female), age (20’s, 40’s, and 60’s), and height (approximately 5, 50, and 95%tile of Japanese male and female). The reduction of muscle strength due to aging was imitated by changing the maximum muscle force of the DHM based on a physical fitness measurement. The elder models (i.e., 40’s and 60’s) showed higher muscle activity of trunk muscles compared with the 20’s model, whereas the muscle activity of lower limb muscles decreased with increase of age. The L5/S1 compression forces of elder models for the male and female models were approximately 22% and 15–30% higher compared with those of 20’s, respectively. The trunk flexion angle of estimated working posture increased with increase of model’s height, and the L5/S1 compression forces of 50%tile and 95%tile models showed approximately 6–17% higher than that of 5%tile model. In addition, the NLE may underestimate the risk of low back pain when the horizontal distance of handled material is far.