Date of Award

May 2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Kinesiology

First Advisor

Stephen C Cobb

Committee Members

Kristian M O'Connor, Brooke A Slavens, Kevin G Keenan

Keywords

co-activation, Curb, Elderly, kinematics, kinetics, multi-segment foot model

Abstract

The purpose of this dissertation was to identify modifiable lower extremity kinematic and neuromuscular factors associated with step clearance and foot placement during transition step negotiation in older adult females with a history of falling. Specifically a full understanding of the contributions of bilateral joints of the hip, knee, and ankle during step clearance and landing was investigated (Chapter 2). Additionally to further understand how the task is accomplished, we examined the neuromuscular demands required to perform the previously mentioned kinematics (Chapter 3). Finally, to expand upon the knowledge of the multi-segment foot, the kinematics of the distal foot were examined during the landing phase of single step descent (Chapter 4).

Participants were 15 young adult females (18-40 years), 15 older adults without a history of falls in the last year (65+ years), and 15 older adults with a history of at least one fall in the previous year (65+ years). Three-dimensional motion capture and electromyography was collected as participants walked at their self-selected pace on a 5.5 m long raised walkway, descended (via forefoot landing) the 17 cm step leading with the right foot, and continued to walk 3 m.

It was anticipated older women with a history of falls would have the smallest lead and trail limb clearance and closest foot placement before and after the step followed by the older non-fallers and then the young adults. For lead limb clearance and placement, these differences were expected to be the result of greater extension of the lead (swing) limb hip, knee, and ankle and increased flexion (and hip adduction) of the trail (support) limb in the older adult groups. This was not the case; the only difference found was by age with older adults with closer lead limb placement which was accomplished though greater knee flexion. The closer landing may function to reduce single limb stance time during the transition step negotiation to compensate for age-related decreases in lower extremity strength. However, the more flexed knee position may also increase the risk of a fall due to lead limb collapse, as there is an increased reliance on muscular strength rather than skeletal structure for stability.

Regarding the neuromuscular activity, a distal to proximal shift of peak joint moments and powers in older adults, consistent with that established during level walking, was predicted during transition step descent. This bilateral distal to proximal shift in lower extremity joint moments and powers was anticipated to be associated with increases in the co-activation patterns of the knee and ankle musculature during step negotiation. In actuality, no differences were found for either lead or trail limb moments or co-activation levels. However eccentric powers of the lead limb hip and knee were significant with older adults producing decreased power, while the peroneal activation as anticipated, was significantly greater in the older groups. This demonstrates single step descent does not follow the typical distal to proximal shift of moments and powers across age seen during level walking. However, it does establish significant normalized peroneal activation differences across age, which may be due to decreased peroneal strength.

For the distal foot, the older groups were hypothesized to demonstrate increased distal foot plantarflexion (rearfoot, medial midfoot, lateral midfoot, medial forefoot, lateral forefoot) and inversion (rearfoot, medial and lateral midfoot) at initial contact compared to the young group. Further, the older fall history group was anticipated to land with the distal foot more plantarflexed and inverted than the older non-fallers. During the landing phase, the older adult groups were hypothesized to demonstrate smaller ranges of motion in the knee and hip and greater ranges of motion across the distal foot joints in both the sagittal and frontal planes compared to the young group. The distal changes were anticipated to be due to the differences in the initial contact positions and age-related decreased strength of the foot and ankle musculature. Despite previous findings that older adults land from a single step in a more plantarflexed position, this study found across the ankle as well as the distal foot, initial contact angles are similar across groups. Regarding the range of motion of the distal joints from initial contact through weight acceptance, only the midfoot demonstrated differences with the older groups dorsiflexing less than the young adult group at the lateral midfoot, while at the medial midfoot, the older non-fallers actually plantarflexed slightly while the young adults dorsiflexed. Overall, although only statistically significant at the midfoot range of motion, it is possible these differences are due to age-related changes within the joint structures of the distal foot.

The results of this dissertation contribute to the development of falls rehabilitation or prevention programs that are more specifically tailored to address the specific kinematic and neuromuscular dysfunctions contributing to step negotiation falls risk in older adult women.

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