Sex-dependent differences in lumbo-pelvic coordination for different lifting tasks: A study on asymptomatic adults.
During manual material lifting, the sagittal motion is mainly characterized through the lumbo-pelvic coordination, which is quantified by the ratio between the lumbar and hip rotations (L/P ratio). Alteration in the L/P ratio is an important indicator for low back pain (LBP). Previous studies demonstrated sex-dependent differences in LBP prevalence during lifting activities. However, the sex-dependent differences in the L/P ratio during different lifting tasks has to data not been investigated. An optoelectronic system was used to measure the sagittal lumbo-pelvic motion in 10 males and 10 females. Task A was lifting one weight from the ground in front of the body to three target heights with straight knees (A1-3: abdomen, chest and head levels, respectively). Task B was lifting two identical weights from the ground at the sides of the body to three target angles with bended knees (B1-3: arms close and 45° and 90° abducted to the trunk, respectively). Lifts of 10 kg (males and females) and 20 kg (males only) were performed and three phases were investigated: Phase 1 - pure flexion without load, Phase 2 - lifting up weights, Phase 3 - lowering down weights. Females generally displayed a smaller L/P ratio than males. In Phases 2 and 3, the L/P ratio was greater than in Phase 1 for Tasks A and B. The L/P ratio increased with a greater lifting height for Task B, but displayed no difference neither between lifting 10 kg and 20 kg, nor between weight lifting and lowering for both tasks. These results can provide indications for sex-specific recommendations for safer lifting activities.