A large proportion of industrial injuries results from material handling and lifting tasks. Back injuries occur with great frequency, often cause acute suffering and serious disability in the works involved, and are extremely costly to the industrial economy. The objectives of this research are (1) to analyze the three- dimensional force systems that act in the human spine during industrial handling and lifting tasks, (2) to analyze the mechanical stresses within the intervertebral motion segments caused by these systems, and on the basis of this information, (3) to recommend methods for handling and lifting, and limitations on loads so that excessive stress levels in the spine can be avoided. Basic features of the program are (1) the use computer-generated analogs of the entire thoracolumbar spine and finite-element models of single intervertebral motion segments, and (2) the use of data from actual industrial situations to ensure that the models are valid, and to confirm predictions made from model-obtain results. The results of these studies may lead to significant breakthroughs in learning how the incidence of industrial back injuries can be reduced.