THE EFFECTS OF ABDOMINAL MUSCLE COACTIVATION ON LUMBAR SPINE STABILITY

Study Design. A biomechanical model of the lumbar spine was used to ca lculate the effects of abdominal muscle coactivation on spinal stabili ty. Objectives. To estimate the effects of abdominal muscle coativatio n on lumbar spine stability, muscle fatigue rate, and lumbar spine com pression forces. Summary of Background Data. The activation of human t runk muscles has been found to involve coactivation of antagonistic mu scles, which has not been adequately predicted by biomechanical models . Antagonistic activation of abdominal muscles might produce flexion m oments resulting from abdominal pressurization. Qualitatively, antagon istic activity also has been attributed to the need to stability the s pine. Methods. Spinal loads and spinal stability were calculated for m aximum and submaximum (40%, 60% and 80%) efforts in extension and late ral bending using a previously published, anatomically realistic biome chanical model of the lumbar spine and its musculature. Three differen t antagonistic abdominal muscle coactivation patterns were imposed, an d results were compared with those found in a model with no imposed co activation. Results. Results were quantified in terms of the sum of cu bed muscle stresses (Sigma sigma m(3), which is related to the muscle fatigue rate), the maximum compressive loading on the lumbar spine, an d the critical value of the muscle stiffness parameter (q) required fo r the spine to be stable. Forcing antagonistic coactivation increased stability, but at the cost of an increase in Sigma sigma m(3) and a sm all increase in maximum spinal compression. Conclusions. These analyse s provide estimates of the effects of antagonistic abdominal muscle co activation, indicating that its probable role is to stabilize the spin e.