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UBC Theses and Dissertations

The perception and control of weight distribution during sit-to-stand in hemiparetic individuals : can asymmetry be attributed to a sense of effort? Sullivan, Jennifer Lindsay


Hemiparetic stroke survivors often produce asymmetric forces when performing bilateral tasks, despite their perception that the forces are equal. It has been hypothesized that this asymmetry is due to the use of effort – as opposed to force magnitude – as the controlled parameter in bilateral force-matching. That is, human perception of force and weight seems to be based more on the intensity of the outgoing motor command than on afferent feedback. This thesis is focused around an experiment that investigated whether this sense of effort (SOE) plays a dominant role in the control and perception of weight distribution during a functional task, sit-to-stand (STS). Eight chronic stroke survivors and eight healthy controls performed a series of STS trials using a robotic assist device, which employed a rate-controlled, 1-degree-of-freedom rotating seat to allow users to perform the STS movement without having to support their entire body weight. The amount of assistance provided by the device was varied across trials in order to measure STS weight distribution in the context of large, medium, and small load magnitudes. The influence of SOE on the control strategy was assessed by evaluating whether or not the proportion in which the load was distributed between limbs was constant across all load magnitudes. Two types of linear models were fit to each group’s data to quantify the relationship between weight distribution and load: one treating the slope as a fixed parameter, and one incorporating an interaction term. Results suggest that while SOE does influence the employed sensory-motor strategy, afferent feedback is a factor as well. Furthermore, the relative contributions of centrally-generated versus peripherally-generated signals varies among individuals: specifically, SOE has a larger influence on the control strategy of individuals who are more symmetric than those who are more asymmetric. Based on these results, we recommend that improving stroke survivors’ awareness of their movement asymmetries and targeting their perceptual inaccuracies in therapy may serve to facilitate and expedite the rehabilitation process.

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