The effect of spinal fixation of the lumbar motion segment on the changes in the pattern of paraspinal muscle activity and thoracolumbar fascial tension was investigated using a previously developed musculoskeletal model. The paraspinal muscle activity and fascial tension were calculated based on a hypothesis, the intervertebral disc was assumed to have a transducer function and the muscle is activated according to a sensor driving control mechanism to maintain the spinal stability. The analyses were conducted in 60° trunk flexion. For the fixation of the motion segment, a rigid fixation or a dynamic stabilization was applied at L3-L4 or L4-L5 level. As a result, the muscle activities and fascial tension were properly adjusted for lumbar stability and to maintain the trunk flexion.