The mean values of the low back compression and shear forces are shown in Table 1. In the comparison between conditions with and without the instruction to increase pelvic forward tilt, the paired t-test showed there was a significant decrease in low back compression force in the squat posture with the instruction to increase pelvic forward tilt, but not in the stoop posture. In addition, one-way repeated-measures ANOVA and the post hoc test showed there was a significant increase in the low back compressive force in the squat posture without the instruction to pelvic forward tilt, compared the other 3 conditions. The mean increase peak values of the low back compression force in the present study were compared with the safety limit recommended by NIOSH, which is 3400 N. Low back compression force exceeded the safe limit under all 4 conditions.