IMPAIRED BALANCE CONTROL IN PARAPLEGIC SUBJECTS

Postural muscle use during sitting balance control was studied in pers ons with a complete thoracic spinal cord injury (SCI). It was hypothes ized that these subjects use non-postural muscles such as the latissim us dorsi (LD) and trapezius pars ascendens (TPA) to restore sitting ba lance, whereas non-SCI subjects primarily use their erector spinae (ES ). This adaptive postural strategy in SCI subjects presupposes stabili zing 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 tho racic SCI, high thoracic SCI or non-SCI participants. Centre of pressu re changes and activity of the LD, TPA, PM, SA, ES and oblique abdomin al (OA) muscles were measured during task execution. Because non-SCI s ubjects 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 tho racic part of the ES more in situations of similarly perturbed sitting balance than non-SCI subjects. Differences are smaller in the low tho racic SCI group. A kinematic concept combining alternative postural mu scle activity and altered movement in thoracic SCI subjects is discuss ed. (C) 1997 Elsevier Science Ltd.