Interappendicular neurological coupling during various locomotor tasks in persons with and without spinal cord injury

It has been proposed that during human locomotion the neurological coordination between the upper and lower limbs is accomplished largely within the spinal cord, but the functional implications of spinal limb coupling during walking have not been fully explored. The purpose of this study was to determine the influence of upper limb actions on muscle activity during various locomotor tasks. Eleven neurologically intact persons (nonSCI) and six persons with spinal cord injury (SCI) walked on a treadmill while their arm were swung (Swing), fixed on parallel bars (Hold), and held in a similar yet unsupported position as in the parallel bar condition (Sham). In an attempt to match the lower body kinetic and kinematic environment between conditions a body weight support system was used to unload the participants. Plantar forces (Pf) and surface electromyography (sEMG) of six lower limb muscles was measured and averaged for 12 steps for each condition. In nonSCI no statistical differences were observed for any of the measures in response to different arm actions. In the SCI group integrated sEMG of the medial gastrocnemius was greater in Swing compared to Hold at a point when mechanical loading of the legs was not different. A case comparison of persons with SCI suggests that the Hold condition attenuates sEMG and that responsiveness to arm actions are dependent on neurological level and extent of injury