Effects of Various Instructions about Lifting Motion with Different Weights on Hip Joint, Knee Joint, and Trunk Tilt Angles

Abstract

This study investigated the effects of various instructions about lifting motion with different weights on hip joint, knee joint, and trunk tilt angles. Twelve healthy males without back pain performed a lifting motion of a 5kg or 15kg weight from the floor and placing it on a table. Each of the joint angles during the lifting motion were compared regarding three different motion instructions: (1) instructed to hold the weight while lowering the hips and lift it (focusing on hip position; HIP-INST) , (2) instructed to squat and hold the weight while keeping the back straight and lift it (focusing on upper body posture; UB-INST) , and (3) without motion instruction (NO-INST) . Hip joint angles were significantly larger in the UB-INST than in the NO-and HIP-INST. Knee joint angles were significantly larger in the NO-INST than in the HIP-and UB-INST. Trunk tilt angles were significantly smaller in the HIP-and UB-INST than in the NO-INST, and in the UB-INST than in the HIP-INST.Knee joint angle tended to be larger and trunk tilt angle was significantly larger when lifting 15kg than lifting 5kg. These results suggest that the hip and knee joints were flexed and extended in the HIP-INST. Therefore, the instruction focusing on the position of the hips may help to prevent back pain during lifting motions. The results also suggest that instruction regarding such lifting motions might be important when lifting heavier objects.