Compensatory muscle activity for sitting posture during upper extremity task performance in paraplegic persons.

Compensation for the loss of postural activity of the erector spinae (ES) muscle in spinal cord injured (SCI) subjects was investigated. All SCI subjects had clinically complete lesions below the T3 level. Body disbalance was invoked by requiring sitting subjects to execute reaching movements over individually predetermined distances in a horizontal plane. Myoelectric activity of the latissimus dorsi (LD) muscle and the trapezius pars ascendens (TPA) muscle both in the SCI subjects and in controls was recorded. The body disbalance was measured in terms of changes in the position of the body centre of gravity. The effects of anticipation for body displacement were examined by cuing the direction of the reaching movement. Our results indicate that paraplegic subjects use both LD and TPA to stabilize their sitting posture, in contrast to non-disabled persons. Secondly, the movement anticipation is in general slower in persons with paraplegia. Furthermore, the paraplegic subjects showed considerable impairments concerning the processing of precued information prior to a goal-directed upper extremity movement.