Lifting style and participant's sex do not affect optimal inertial sensor location for ambulatory assessment of trunk inclination

Abstract Trunk inclination (TI) is often used as a measure to quantify back loading in ergonomic workplace evaluation. The goal of the present study was to determine the effects of lifting style and participant's sex on the optimal inertial sensor (IS) location on the back of the trunk for the measurement of TI. Gold-standard TI, defined as the angle between the vertical and the line connecting the L5/S1 joint and the trunk center of mass, was measured using an optoelectronic system. Ten males and ten females performed experimental trials in which a box was lifted from floor level to a 75 cm elevated surface. In each trial the box was lifted using four different styles: symmetric and asymmetric free-style lifts, a stoop lift and a squat lift. Trials were repeated for 13 IS locations between 10% and 40% of the distance from the sacrum to the seventh cervical spinous process (C7). For each participant and each IS location, the root-mean-square error (RMSE) between the gold standard TI and the ISTI was determined. A three-way repeated measures ANOVA analysis revealed no significant effects of the participant's sex on the RMSEs, but the main effects of lifting style and sensor location and their interaction were significant. Despite this significant interaction, a sensor location between 20% and 27.5% of the distance from the sacrum to C7 yielded the smallest RMSEs across all lifting styles. In conclusion, regardless of participant's sex or lifting style, the optimal IS location for the measurement of TI is at about 25% of the distance from the sacrum to C7.