posture shifting after spinal cord injury using functional neuromuscular stimulation—a computer simulation study

the ability for individuals with spinal cord injury (sci) to affect changes in standing posture with functional neuromuscular stimulation (fns) was explored using an anatomically inspired musculoskeletal model of the trunk, pelvis and lower extremities (le). the model tracked trajectories for anteriorly and laterally shifting movements away from erect stance. forces were applied to both shoulders to represent upper extremity (ue) interaction with an assistive device (e.g., a walker). the muscle excitations required to execute shifting maneuvers with ue forces <10% body-weight (bw) were determined via dynamic optimization. nine muscle sets were examined to maximize control of shifting posture. inclusion of the psoas and external obliques bilaterally resulted in the least relative ue effort (0.119, mean ue effort=45.3 n=5.4% bw) for anterior shifting. for lateral shifting, the set including the psoas and latissimus dorsi bilaterally yielded the best performance (0.025, mean ue effort=27.8 n=3.3% bw). however, adding the psoas alone bilaterally competed favorably in overall best performance across both maneuvers. this study suggests suitable activation to specific muscles of the trunk and le can enable individuals with sci to alter their standing postures with minimal upper-body effort and subsequently increase reach and standing work volume.