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Postural control and falls in individuals with chronic stroke : neural mechanisms and effects of exercise Marigold, Daniel S.

Abstract

Although falls and fall-related injuries are an enormous burden for individuals with stroke, we do not know the neural mechanisms underlying these events. While impairments in postural control presumably contribute to falls, the type of exercises most effective for improving postural control in individuals with chronic stroke are unclear. The purpose of this thesis was (1) to understand how individuals with chronic stroke modulate postural control and determine the underlying neural mechanisms contributing to falls and (2) to determine the effects of two different exercise interventions on postural control and physical function. In each of the three experiments conducted, postural reflexes were evoked by unexpected translations of a platform upon which participants were standing. Experiment I examined the effects of different weight-' bearing load on the modulation of lower limb postural reflexes. We revealed that individuals with stroke could modulate ankle extensor, but not ankle dorsiflexor reflex magnitude. In Experiment II we discovered that reduced tibialis anterior reflex magnitude and delayed nonparetic rectus femoris onset latency contribute to falls in individuals with stroke. In addition, reduced maximum volitional muscle strength, particularly the paretic lower limb, contributed to falls induced by platform translations. Based on the results from the first two experiments, we hypothesized that deficits in supraspinal centres are responsible for the impaired postural control observed. Experiment HI was a 10-week randomized clinical trial in individuals with chronic stroke. The results demonstrated that regardless of intervention (Agility or Stretching/weightshifting program), exercise resulted in faster paretic lower limb postural reflexes, improved functional balance and mobility, faster step reaction time, and improved balance confidence and quality of life. However, there was a greater change in paretic rectus femoris postural reflex onset latency and step reaction time for the Agility exercise group. Although there was no difference in the number of fallers between groups when the entire sample was included, a subanalysis of those with a history falls demonstrated a reduction in the number of fallers in the Agility group. These results suggest that an Agility-based exercise intervention may be more beneficial for individuals with stroke. Further, the results suggest exercise-induced neural plasticity.

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