Compressive loads in the lumbar vertebral column during normal level walking.

The longitudinal compressive load acting on the L3-L4 spinal motion segment was investigated during normal level walking for a range of speeds of progression. Forces were predicted using experimental data from photogrammetric measurements of upper body segmental motion and inertial properties, along with a biomechanical model of the trunk. A partial validation of the results was obtained using records of the electrical activity of the trunk muscles and intradiscal pressure information available in the literature. Experiments were carried out in five normal young male subjects. Results showed that the L3-L4 motion segment is subjected to cyclic compressive loads. The maximum and minimum values of this load vary with walking speed from approximately 1.0 to 2.5 and from 0.8 to 0.2 times body weight, respectively. Relevant peaks occur with a frequency ranging approximately from 1.3 to 2.5 Hz. Muscular action is mostly concentrated in the trunk extensors, which show a burst of activity at the time of ipsilateral toe-off.