Paraplegic standing controlled by functional neuromuscular stimulation. II. Computer simulation studies

For pt.I see ibid., vol.36, no.9, p.873-84 (1989). Two types of body motion are simulated. The body position is assumed to be initially perturbed from the upright position, and all muscles are assumed inactive at the initial position. The control law developed in pt.I drives the body segments to the standing position. Arm movements are then applied to the body to investigate how performance is affected by an external disturbance. Simulated body motion indicated that the current output-feedback control law functions well. The body can recover upright posture from a highly fixed position, and the controller can then maintain the body near the vertical during arm movements. The simulation results showed three consistent activation patterns based on energy minimization: (1) no antagonistic muscle pairs are coactivated, (2) strong muscles are recruited before weak ones, and (3) fast muscles are recruited before slow ones.