Spinal loading during manual materials handling in a kneeling posture

Stooped, restricted, kneeling, and other awkward postures adopted during manual materials handling have frequently been associated with LBP onset. However, lift assessment tools have focused on materials handling performed in an upright, or nearly upright standing posture. Unfortunately, many of the tools designed to analyze standing postures are not easily adapted to jobs requiring restricted postures. Therefore, the objective of this study was to evaluate spinal loading during manual materials handing in kneeling postures and determine if those loads can be predicted using simple regression. An EMG-driven biomechanical model, previously validated for upright lifting, was adapted for use in kneeling tasks. Subjects knelt under a 1.07 m ceiling and lifted luggage of six weights (6.8, 10.9, 15.0, 19.1, 23.1 and, 27.2 kgf) to one of four destination heights (0, 25.4, 53.3, 78.7 cm). Spine loading was significantly affected by both destination height and load weight. Destination height increased compression, AP shear and lateral shear by an average of 14.5, 3.7 and 6.6 N respectively per cm height increase. Load weight increased compression, AP shear and lateral shear by an average of 83.8, 27.0 and 13.1 N respectively per kgf lifted. Regression equations were developed to predict peak spine loading using subject height, load weight and destination height with R2 values of 0.62, 0.51 and 0.57 for compression, AP and lateral shear respectively.