Approximately one in three adults over 65 fall annually, with the majority of these falls occurring during locomotion. The underlying causes of these falls could include a number of physiological factors such as age-related declines in sensory acuity, executive function, cognitive capacity, muscle strength and reaction time. Prior studies have identified links between gait variability metrics, dynamic balance and fall risk in older adults. Step width variability is particularly relevant given the inherent challenge in modulating step width to maintain medio-lateral balance during walking. However, challenging walking tasks may be required to elucidate increases in gait variability that arise from subtle age-related changes in cognitive processing and sensorimotor function. This dissertation investigated how visual, cognitive and physical challenges can affect gait variability and muscle coordination in healthy old adults.

The first study investigated the relative effects of perturbed visual feedback, increased cognitive load, and narrowed step width demands on gait variability in healthy old and young adults. Eleven healthy old (OA, average age 71.2 ± 4.2 years) and twelve healthy young (YA, 23.5 ± 3.9 years) adults walked on a treadmill while watching a speed-matched virtual hallway. Subjects walked 1) normally, 2) with medio-lateral visual perturbations, 3) while performing a cognitive task (serial seven subtractions), and 4) with narrowed step width. Motion capture was used to track step width and length over three minutes of walking for each condition. Old subjects were most sensitive to the visual perturbations, with step width variability increasing more than 150% relative to the normal condition. The cognitive task and walking with narrowed step width did not show any effect on step width or length variability in either group. The dramatic increase in step width variability when old adults were subjected to medio-lateral visual perturbations was likely due to an increased reliance on visual feedback for assessing whole body position with aging.

The second study investigated how old adults modulate lower extremity muscle coordination patterns when presented with challenging walking tasks. It was hypothesized that old adults would have greater muscle co-activation than in young adults in normal, unperturbed walking. Further, it was hypothesized that old adults would increase their use of a co-activation strategy to stiffen joints in walking tasks that challenge balance. Electromyographic (EMG) activity was recorded bilaterally from the medial hamstring (MH), vastus lateralis (VL), medial gastrocnemius (MG), soleus (SL), and tibialis anterior (TA) muscles. Muscle co-activation for MH-VL, MG-TA, and SL-TA pairs were computed. In contrast to some prior studies, old adults in this study exhibited muscle activation patterns that were generally similar to young adults during normal walking at self-selected speed. However, the visual perturbation condition significantly increased muscle co-activation in the old adults, both in comparison to normal walking and relative to young adults. It was concluded that aging is associated with an increased reliance on visual information to maintain balance during walking, with inaccurate visual information causing old adults to adapt their coordination to accommodate the perceived threat to balance.

The final study investigated a noninvasive neuromodulation approach for enhancing gait and balance in old adults. There remains a substantial need for effective balance training programs given the substantial medical and personal costs associated with fall-related injuries. Prior studies have shown that traditional exercise programs can enhance strength in old adults, but that these improvements generally don’t translate to improved balance and reduced fall risk. This finding would suggest that deficits in sensory function and sensori-motor integration may be better targets for enhancing balance in old adults. Cranial nerve non-invasive neuromodulation (CN-NINM) is a relatively new technology for enhancing neuroplasticity, which in turn could improve sensorimotor processes. CN-NINM uses electrical stimulation of cranial nerve endings in the dorsal surface of the tongue to heighten activity in the brainstem. Prior studies suggest that coupling CN-NINM with gait and balance training may enhance the therapeutic benefits in subjects with traumatic brain injury and multiple sclerosis compared to standard gait and balance therapy. A pilot study of the efficacy of CN-NINM for training gait and balance in old adults was performed. Sixteen old adults (ages 66-80) participated in a double-blind randomized, controlled study. All subjects participated in a 10-day supervised gait and balance training intervention. Half of the subjects (active group) performed the intervention exercises with an active CN-NINM device, while half used a device that delivered only sub-sensory stimulation. Clinical and quantitative assessments of gait variability and postural balance were performed before and after the 10-day intervention. There were significant improvements in gait and balance metrics after training. After the intervention, subjects exhibited reduced step width variability when subjected to visual perturbations during walking. Further there were some reductions in standing sway measures. However, there were no significant differences in post-training metrics between the active and control groups. It is noted that the subjects who participated were generally healthy and physically active with limited history of falling. Future studies should consider the potential benefits of CN-NINM in old adults with a history of falls, given their greater potential for improvement.