Experimental and biomechanical model force fields produced by intraspinal microstimulation of the cat lumbar spinal cord

Using a biomechanical model of the cat hindlimb, we studied patterns of endpoint forces created by all muscle combinations of fourteen selected muscles, and compared them to the force patterns produced by intraspinal microstimulation of the lumbar spinal gray matter. We ran the model with two different activation schemes for the muscles. The first run used combinations of the fourteen selected muscles stimulated at the same level of activation. The second run used combinations where muscle forces were normalized to produce the same maximum end-point force. These results were compared to force field patterns obtained experimentally during intraspinal microstimulation. Although there were slight variations in the force patterns produced, both methods converged to four dominant patterns. When muscles in the model were normalized, some force patterns were found that were not observed experimentally. These results show the significance of specific levels of muscle activation to the production of the experimental patterns.