EFFECT OF AGE AND FALL STATUS ON THE SCALING OF THE POSTURAL CONTROL VARIABLES TO A SCALED GAIT INITIATION TASK

Abstract

Inefficacy of the postural control system can lead to loss of equilibrium and upright stability, and ultimately a fall by older adults. Understanding the control of the center of mass (CoM) with respect to the base of support (BOS) in a progressively challenging environment that encourages individuals to scale postural control variables is of clinical importance. Subsequently, the long-term goal of this work is to optimize evidence-based balance rehabilitation programs for older adults with balance impairments. However, it is currently unclear how older adults perform scaled tasks during gait initiation (GI). It is possible that older adults with a fall history would have problems scaling postural control variables in response to scaled postural challenges. The inability to scale postural control variables could further increase their chance of becoming unstable. Therefore, the purpose of this dissertation was to understand how older adults control balance in postural challenging GI tasks such as scaled step distance and step width tasks. The scaled step distance task involved stepping over an obstacle placed at progressive distances from an individual’s body. The scaled step width task involved stepping over an obstacle and stepping on medial or lateral targets placed on the floor. In the first study, we observed healthy adults (n = 17 with a mean age of 27.8 ± 6.3 years) performing scaled GI tasks in the presence of an obstacle in the sagittal plane. Overall, healthy adults increased anterior-posterior (AP) center of mass-center of pressure (CoM-CoP) displacement and decreased trunk forward lean at maximum CoM-CoP displacement during swing in response to scaled GI tasks. As a part of an exploratory analysis, we also found that the variability of AP CoM-CoP displacement at maximum CoM-CoP displacement during swing did not change, but the variability of trunk lean at maximum CoM-CoP displacement during swing increased. The findings suggest that healthy adults scale the AP CoM-CoP displacement and the AP trunk lean per the task demand. For our second study, we compared the scaling behavior of postural control variables in the sagittal plane between older non-fallers (n = 12 with a mean age of 73.41 ± 3.91 years) and fallers (n = 12 with a mean age of 71.66 ± 5.53 years) while performing scaled GI tasks in the presence of an obstacle in the sagittal plane. In this study, we found that older fallers reduced AP CoM-CoP displacement prior to the toe-off compared to non-fallers. However, at maximum CoM-CoP displacement during swing, AP CoM-CoP displacement was not different between the groups. We also found that older fallers increased peak trunk forward lean during swing compared to non-fallers. These findings suggest that older fallers adopt a greater conservative approach with AP CoM-CoP displacement than non-fallers prior to the toe-off of the scaled GI task to compensate for instabilities that may arise due to the peak AP trunk lean in the swing phase. In our third study, we compared scaling differences between older non-fallers (n = 12 with a mean age of 73.41 ± 3.91 years) and fallers (n = 8 with a mean age of 70.62 ± 5.26 years) during scaled step width GI tasks in the frontal plane. We found that older fallers reduced medial-lateral (ML) CoM-CoP displacement at maximum CoM-CoP displacement during swing compared to non-fallers. However, the groups were not different prior to the toe-off of the GI tasks. We also noted that older non-fallers increased trunk tilt toward the stance limb more in the obstacle than the no obstacle condition irrespective of step width conditions, whereas fallers had increased trunk tilt toward the stance limb irrespective of the obstacle presence or step width conditions. These findings suggest that older fallers adopt a greater conservative approach for the ML CoM-CoP displacement and ML peak trunk tilt than non-fallers during the swing phase of scaled GI tasks for scaled step width conditions. This study provides a framework for investigating postural stability in older adults with clinical problems in a laboratory setting. Looking at a broader comparison between healthy adults (less than 40 years of age) and older adults (above 65 years of age) with the scaled step distance tasks during GI, it seems that older adults prefer a cautious strategy based on CoM-CoP displacement at maximum CoM-CoP displacement during swing than healthy adults. Furthermore, young adults and older adults, whether non-fallers or fallers, approach in a way that they can complete the task successfully while ensuring safety. The results of these investigations show that changes in the CoM-CoP displacement are dependent on the phase of the GI tasks and plane in which the variable was examined. This study’s findings may be used to identify postural instability and design targeted balance rehabilitation protocol in balance-impaired populations, such as older adults, children with cerebral palsy, and other neurological populations.