A dynamic biomechanical evaluation of lifting maximum acceptable loads

J Biomech. 1984;17(4):251-62. doi: 10.1016/0021-9290(84)90136-2.


A biomechanical evaluation of the job-related stresses imposed upon a worker is a potential means of reducing the high incidence rates of manual material handling injuries in industry. A biomechanical model consisting of seven rigid links joined at six articulations has been developed for this purpose. Using data from cinematographic analysis of lifting motions the model calculates: (1) body position from articulation angles, (2) angular velocities and accelerations, (3) inertial moments and forces, and (4) reactive moments and forces at each articulation, including the L5/S1 joint. Results indicated effects of the common task variables. Larger load and box sizes increased the rise times and peak values of both vertical ground reaction forces and predicted L5/S1 compressive forces. However, boxes with handles resulted in higher L5/S1 compressive forces than for boxes without handles. Also, in lifting the larger boxes the subjects did not sufficiently compensate with reduced box weights in order to maintain uniform L5/S1 compressive forces. Smoothed and rectified EMG of erector spinae muscles correlated significantly with L5/S1 compressive forces, while predicted and measured vertical ground reaction forces also correlated significantly, indicating the validity of the model as a tool for predicting job physical stresses.

MeSH terms

  • Humans
  • Joints / physiology*
  • Models, Biological
  • Muscles / physiology*
  • Physical Exertion
  • Posture
  • Spine / physiology*
  • Stress, Mechanical*