Year of Award

2016

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Individualized Interdisciplinary Doctoral Program

Department or School/College

Interdisciplinary Studies Program

Committee Chair

Charles T. Leonard

Commitee Members

Gayle Hudgins, Jonathan Graham, Matthew Bundle, Michael P. Kavanaugh

Abstract

Episodes of instability and falls in the elderly represent a major public health concern. The lack of scientific information about the effects of age-related changes on neurophysiological mechanisms of postural control has limited the advance in the field of fall prevention and rehabilitation of balance disorders. The overall goal of this dissertation was to investigate the effects of aging on postural control. Considering the progressive non-homogeneous deterioration of aging physiological systems, a series of five experimental studies, with healthy young and healthy nonfaller older adults performing upright stance tasks, explored three main hypotheses: (1) intermuscular coherence analysis is able to detect signs of intermuscular synchronization at lower frequency bands as one of the strategies used by the Central Nervous System to control upright stance; (2) aging is associated with a reorganization of correlated neural inputs controlling postural muscles; and (3) aging is associated with changes in body sway behavior. The first three studies corroborated the use of intermuscular coherence analysis to investigate the formation of correlated neural inputs forming postural muscle synergies during upright stance. The fourth study revealed an age-related reorganization of the distribution and strength of correlated neural inputs to multiple postural muscles. Healthy nonfaller older adults presented stronger levels of synchronization, within 0–10 Hz, for three distinct muscle groups: anterior, posterior, and antagonist muscle groups. The fifth study investigated age-related changes on postural sway using traditional and novel postural indices extracted from the center of pressure coordinates. Although the functional base support is preserved in healthy nonfaller older adults, these seniors revealed a larger, faster, shakier, and more irregular pattern of body sway compared to healthy young adults. In addition, age-related changes on supraspinal mechanisms, spinal reflexes, and intrinsic mechanical properties of muscles and joints involved in postural control were observed by changes in both rambling and trembling components of the postural sway. Findings reported here provide valuable information regarding compensatory mechanisms adopted by healthy nonfaller older adults to control upright stance. Together, these findings suggest an age-related reorganization of correlated neural inputs controlling multiple postural muscles, accompanied by changes in body sway behavior.

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© Copyright 2016 Adriana Menezes Degani