Neuromuscular Control of the Trunk during Sitting Balance

Sitting stability is maintained by continuous and intermittent activation of trunk and lower limb muscles. However, spinal cord injury (SCI) can result in paralysis of the trunk muscles and affects sitting balance. Currently, chest straps and trunk braces are used to correct sitting after SCI. In addition to these passive devices, functional electrical stimulation (FES) could be used to artificially contract trunk muscles and regulate sitting balance. The objectives of this research project were to: (1) investigate neuromuscular synergies of the trunk during perturbed sitting; (2) investigate the effects of anticipation of the perturbation on trunk muscle responses; (3) compare sitting balance between able-bodied individuals and people with SCI; and (4) examine the effects of electrical stimulation of trunk muscles on sitting balance. The first deliverable (Chapter 2) of this project was the development of neural network models that encode trunk muscle responses during perturbed quiet sitting. These models describe complex neuromuscular synergies of the trunk and allow us to understand which muscles are used to stabilize sitting balance. The second deliverable (Chapter 3) was a study which showed that anticipation of direction and time of perturbation resulted in approximately 15 ms faster trunk muscle activations. These results indicate that the reflexive and patterned neuromuscular responses of the trunk can be modulated by the central nervous system using anticipatory information. The third deliverable (Chapter 4) was a study that investigated differences in sitting balance between able-bodied individuals and individuals with SCI. This study has shown that trunk control is significantly compromised in individuals with SCI, which is the main cause of their reduced balance control during quiet sitting. The fourth deliverable (Chapter 5) was a study that investigated the effects of FES of trunk muscle on sitting balance control. The results showed that co-contractions of trunk muscles with FES could increase trunk stiffness. These findings combined advanced our understanding of the neuromuscular control of the trunk during sitting balance. Moreover, they helped us develop a neuroprosthesis, which could improve sitting balance in individuals with SCI, and consequently contribute to improving their mobility, independence and, ultimately, quality of life.