The effect of predictable and unpredictable motor tasks on postural control after traumatic brain injury

This study examined the effects of environmental predictability on postural control during functional reaching while seated in healthy individuals and patients with traumatic brain injury (TBI). The postural perturbation used required reaching to the left versus reaching to the right, while seated, under predictable versus unpredictable conditions. Indexes of postural control - trajectory stability and response reach times - were measured using an electromechanical system in ten patients with TBI and ten healthy subjects. In the TBI group, greater trajectory stability and shorter response reach time were recorded under unpredictable conditions when reaching to both the right and left (d-index 0.57-2.3). In the control group, greater trajectory stability and shorter response time were recorded under predictable and unpredictable environments compared with the TBI group (d-index 0.46-0.95). This study refutes the hierarchical, predictable-to-unpredictable-environment model of postural control evaluation and treatment. The relationship between information processing demands and postural skill appears more complex than a simple linear association. Predictable and unpredictable conditions may be used concurrently, not sequentially, in TBI rehabilitation.