Impaired balance control in paraplegic subjects.

Postural muscle use during sitting balance control was studied in persons with a complete thoracic spinal cord injury (SCI). It was hypothesized that these subjects use non-postural muscles such as the latissimus dorsi (LD) and trapezius pars ascendens (TPA) to restore sitting balance, whereas non-SCI subjects primarily use their erector spinae (ES). This adaptive postural strategy in SCI subjects presupposes stabilizing effects of the scapular protractors, such as the pectoralis major (PM) and the serratus anterior (SA), on the shoulder girdle. Sitting balance was perturbed systematically in three groups of either low thoracic SCI, high thoracic SCI or non-SCI participants. Centre of pressure changes and activity of the LD, TPA, PM, SA, ES and oblique abdominal (OA) muscles were measured during task execution. Because non-SCI subjects differ from SCI subjects in their ability to tilt their pelvis during sitting, the correlation between pelvic movement and postural changes during task execution was also investigated. Results indicate that high thoracic SCI subjects use their LD, TPA, PM, SA and high thoracic part of the ES more in situations of similarly perturbed sitting balance than non-SCI subjects. Differences are smaller in the low thoracic SCI group. A kinematic concept combining alternative postural muscle activity and altered movement in thoracic SCI subjects is discussed.