Development of new muscle synergies in postural control in spinal cord injured subjects.

The development of new patterns of postural control in patients with a complete thoracic spinal cord injury (SCI) during their active clinical rehabilitation was studied. Especially the role of non-postural muscles, like the latissimus dorsi (LD) and the trapezius pars ascendens (TPA), in maintaining and restoring sitting balance during standardized bimanual task performance was investigated. Twelve patients, diagnosed with an acute complete thoracic SCI between spinal cord level T2 and T12, participated in a longitudinal experimental study. Changes in the centre of pressure (CP) and electromyographic activity of the erector spinae (ES) at level L3, T9 and T3, the LD, the TPA, the pectoralis major (PM), the serratus anterior and the oblique abdominal muscles were investigated at several moments in the rehabilitation process. Results show a gradual development of specific muscle activation patterns for both high and low thoracic SCI patients. These patterns seem to be related to a combination of restoration of function of the ES-L3 and ES-T9 in the low thoracic SCI subjects and increased compensatory muscle use of the LD, TPA and PM in high SCI patients. The range in which low thoracic SCI patients can actively vary their CP increased slightly during rehabilitation.