2006 Volume 57 Issue 2 Pages 101-111
The objective of this study was to identify the differences in some kinetic parameters among task conditions during asymmetric load-lifting tasks. The lifting motions were filmed by two high-speed video cameras. The moments were measured by a force plate. Three independent variables were manipulated in this study: horizontal distance from a subject to the box being lifted at the start of lifting (initial distance: 30cm and 60cm), height lift (65cm and 105cm), and weight of the box (4kg and 12kg). All factors were within-subject variables. The motion characteristics of the wrist joints, elbow joints, shoulder joints, hip joints, knee joints, and ankle joints on both the right and left sides were obtained on the basis of the reconstructed data of these points by the Direct Linear Transformation (DLT) method. Based on the reconstructed 3-D data and the moments, kinetic parameters such as the power of both forearms and both upper arms, and spinal loads such as the compression force F_c, anterior/posterior shear force F_<sAP> and the medial/lateral shear force F_<sML> were calculated. The following characteristics of the asymmetric lifting task were revealed regardless of the task conditions: (a) the loading on the lumber spine was the largest at 30% of the normalized time; and (b) increasing the waist-twisting angle significantly increased the medial/lateral shear loading on the lumber spine. Moreover, it was clarified that the kinetic parameters were greatly affected by the three task conditions (initial distance, height, and weight): (a) the initial distance affected the F_c from 0% of the normalized time to 70%; (b) the height affected the spinal loads after 40% of the normalized time; and (c) the weight affected the F_c and F_<sAP> throughout the lifting task and affected F_<sML> after 40% of the normalized time.
