Motor preparation in postural control in seated spinal cord injured people

Spinal cord injured (SCI) people try to compensate for the loss of postural muscle function by increased use of non-postural muscles. Such alternative muscle use, however, may necessitate important modifications in motor cont rol. In this study motor programming processes were investigated in three g roups, i.e. in high thoracic SCI, low thoracic SCI and non-SCI subjects. A bimanual forward-reaching task, in which graded sitting balance perturbatio n was systematically invoked, was presented to the subjects as a visual pre cue choice reaction time (RT) task. Effects of movement preparation were ex amined by precuing reaching distance information. RT and movement times wer e recorded. Centre of pressure (CP) displacement was used as an indicator f or sitting balance perturbation. Results indicated that high thoracic SCI s ubjects programmed balance-perturbing reaching movements as fast as did non -SCI subjects. Low thoracic SCI subjects, on the other hand, showed substan tially longer programming times. This latter outcome is consistent with the hypothesis that the low thoracic SCI subjects adopted a more complex postu ral control strategy involving residual motor functions in an attempt to ac tively compensate for loss of postural muscle function. High thoracic SCI s ubjects, on the other hand, appeared to adopt a less complex and thus easie r to programme postural control strategy.