College of Natural and Health Sciences; School of Sport and Exercise Science, Biomechanics Emphasis
University of Northern Colorado
Type of Resources
Place of Publication
University of Northern Colorado
The overall purpose of this dissertation was to investigate the influence of visual disruption on measures of postural stability, specifically in anterior cruciate ligament reconstruction (ACLR) individuals. Each of the two studies included in this dissertation evaluated postural stability, with the first study evaluating static postural stability and the second study evaluating dynamic postural stability. For the first study, 26 individuals (ACLR group n = 13; control group n =13) were asked to complete both double- and single-limb stances on embedded force platforms while visual information was disrupted using stroboscopic eyewear. Postural stability was assessed using traditional center of pressure (COP) measures. A more recently developed stabilogram diffusion analysis (SDA) was attempted on this group, but data for nearly half of the participants in each group could not be interpreted so this analysis was discarded. Visual information was disrupted using specialized stroboscopic eyewear that cycled through periods of clear and opaque settings. Two visual disruption settings (low and high) along with and eyes-open condition were completed during all stability testing. Group comparisons were performed between individuals with a history of ACLR and healthy, young adults were assessed using standard data analysis. In both double- and single-limb postural stability tasks, demonstrated that ACLR individuals did not rely on visual information to a greater extent than healthy controls. During double-limb stance, ACLR individuals presented with decreased levels of mean COP frequency compared to controls (0.50 ± 0.20 vs 0.69 ± 0.29 Hz). However, no group differences were observed for root mean square distance, mean velocity, and sway area of the COP. No group differences were observed for the single-limb stance condition. Postural stability changes were observed when visual information was disrupted through the use of stroboscopic eyewear, indicating that the glasses were effective at challenging an individual's postural control. For the double-limb stance, the high level of visual disruption resulted in increased mean velocity (14.28 mm/s) compared to the eyes open conditions (13.03 mm/s). All single-limb standard COP measures of postural stability were elevated in the low and high visual disruption conditions when compared to the eyes open condition. The second study’s purpose was to evaluate whether ACLR individuals relied on visual information to a greater extent than healthy controls during a dynamic single-limb hopping task. For the dynamic task protocol, 22 participants (ACLR group n = 11; control group n =11) jumped from a two-footed stance and touched an overhead target before landing in a single-limb position on a force platform. The visual conditions utilized three conditions, eyes open, low visual disruption, and high visual disruption. Dynamic postural stability was evaluated using both standard and SDA measures. No group differences were observed, indicating that ACLR individuals did not present with worsened dynamic postural stability compared to healthy controls. There were significant differences between the visual conditions in both the standard and SDA measures. Only the medial-lateral stability index increased with visual disruption for the standard measures. For SDA measures, both the mean critical square displacement and short-term diffusion coefficient increased with visual disruption, and both short- and long-term scaling exponents decreased with visual disruption. In both studies, the lack of an interaction between the effects of group and vision suggests that ACLR individuals do not rely on visual information to a great extent than control individuals. Additionally, ACLR individuals do not present with worsened postural stability than controls for static or dynamic postural stability tasks. Additionally, this dissertation demonstrated that stroboscopic eyewear perturbed static and dynamic postural stability. The effects of the visual disruption on postural stability had more significant effects during the more challenging single-limb and dynamic postural stability tasks. Based on the current dissertation findings, future research should aim to explore static and dynamic postural stability tasks with activity level matched healthy controls. Future research should also explore the connection between stroboscopic eyewear and sport-like activities to justify their use for laboratory analysis.
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