Neuromuscular aging and frailty
Date
2016
Authors
Fritz, Megan Leigh, author
Tracy, Brian L., advisor
Rudroff, Thorsten, committee member
Reiser, Raoul F., II, committee member
Davalos, Deana, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
The aging process is accompanied by gradual declines in physical and cognitive function. The majority of neuromuscular research has only approached the changes that occur from a chronological aging perspective. The way in which individuals age, however, is not necessarily accounted for in chronological years. Additional factors such as comorbidities, the development of disability, and frailty status play a role in determining successful vs. unsuccessful aging. It is the overall intention of this dissertation to assess aspects of neuromuscular aging within the context of physical frailty and explore potential interventions for improving age- or frailty-associated neuromuscular impairment. The first chapter of this dissertation consists of a review of the proprioception literature. Proprioception is generally the perception of body movement. This afferent system is crucial for maintaining postural stability and reducing fall risk. The first experiment (Chapter II) was designed to assess proprioceptive perception at the ankle joint while comparing young adults, healthy older adults, frail older adults, and adults with comorbidities affecting the peripheral nervous system (peripheral neuropathy) and the central nervous system (stroke). The results indicate that healthy older adults have similar proprioceptive function at the ankle to that of young adults. Those aged with comorbidities such as peripheral neuropathy exhibited the greatest deficits in proprioceptive function. Muscle spindles are considered the primary sensors of joint movement perception, a major component of the overall proprioceptive sense. Vibratory stimulus may alter the afferent signaling of muscle spindles. Robust vibration tends to impair or provide illusory sensations within muscle spindles, while low-level vibration has the potential to enhance muscle spindle sensation. The goal of the second experiment (Chapter III) was to determine if low-level sub-sensory vibration applied to the plantarflexor and dorsiflexor tendons could improve proprioception among healthy young adults. The study demonstrated that sub-sensory vibration did in fact improve ankle joint proprioception and those with the poorest proprioception experienced the greatest benefit from the vibration. The third study (Chapter IV) was designed to assess the potential for the same sub-sensory vibration intervention among healthy and frail older adults. The results indicated that the sub-sensory vibration did not improve ankle joint movement perception in either the dorsiflexion or plantarflexion directions. Frail demonstrated impaired proprioception in both the plantarflexion and dorsiflexion directions compared with healthy older adults. Women exhibited greater (impaired) joint movement perception in the plantarflexion direction compared with the dorsiflexion direction, while men were similar across both directions. Frail women appeared to be driving the significant differences in joint movement perception and therefore may represent the most relevant target population for the proprioceptive interventions.