Examining age-related changes to muscle properties and their relationship with coordinated movement and balance control.

McIntosh, Emily
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University of Guelph

Life expectancy is increasing, but with advanced age comes an elevated risk for sustaining a fall. Individuals with sarcopenia have been shown to fall more frequently, however the mechanism behind this remains unknown. The focus of this dissertation was to examine properties of muscle related to rapid volitional movement. Over the course of four experiments both age-related and sex effects were explored. Measurements were obtained through kinetic, kinematic, anthropometric, and clinical tests. A large focus was on knee extensor muscles due to their importance in activities of daily living, however arm movements during a handrail grasping task were also examined. Young adults were stronger and more powerful than older adults at maximum voluntary knee extension and these increased abilities were associated with larger rates of torque and velocity development. A major age-related difference was a decreased maximal velocity in the older adults relative to the young adults, which was observed in a knee extension task and center of mass velocity during a voluntary reactive task. Males were stronger, faster, and more powerful for nearly every metric examined, however, they were also on average taller, heavier, and leaner than the females. These anthropometric differences are key factors in the observed sex-related differences. Body composition analyses revealed that no older adult tested was classified as sarcopenic, however individuals with low grip-strength were shown to have proportionately lower muscle quality than their peers. Grip strength was significantly correlated to dual task Timed Up and Go time and several reactive movement metrics (e.g. total movement time, peak lateral centre of mass velocity, and total 3-dimensional movement) during a lateral handrail grasping task executed during forward walking. Collective results from this dissertation suggest that older individuals interested in reducing falls risk should consider participation in physical activities that not only promote strength gains but do so with high velocity movements. We also encourage future studies and clinicians to consider incorporating both grip strength and dual-task Timed Up and Go into their protocols as very simple measurements that could aid in the identification of individuals who may be at a greater risk for injurious falls.

Muscle, Aging, Power, Sex Differences, Range of Motion, Balance Response, Velocity