Motor Unit Discharge and Slowed Motor Output in Elderly

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DESCRIPTION (provided by applicant): The elderly are often frustrated by poor control during precision tasks, and slower production of muscular force has specific importance in fall prevention. Motor unit research is in dire need of expanded paradigms to provide new information about control mechanisms during real-world tasks. We will examine age-related differences in two relevant motor unit discharge behaviors and provide information that can be used to improve movement quality in older adults and also in patient populations. Aim 1 is about rate coding during the precise control of sinusoidal isometric contractions. It is hypothesized that that the amplitude of firing rate modulation is less in older adults, perhaps due to enhanced twitch summation of aged muscle fibers with slowed contractility. Aim 2 is about motor unit discharge behavior during rapid force production from rest as well as from a submaximal force level. It is hypothesized that during the initiation of rapid contractions, the initial firing rates of aged motor units will be slower and there will be fewer doublet discharges, as compared to young adults. Motor unit and muscular force recordings, surface electromyography and contractile properties will be obtained from the first dorsal interosseous muscle of 20 young (<30 years) and 20 older (>65 years) adults. Successful experiments in these conditions can be considered significant progress in motor unit research. In addition to furthering knowledge of normal aging at the level of the motor unit, this project will provide vast new information about motor unit discharge behavior in general. Consider for example: 1) the value of this normative data for similar research in patient populations, and 2) a better knowledge of neural commands in healthy individuals can help to improve the functional electrical stimulation of paralyzed muscle. This project also provides the basis for future research on the adaptability of these neural factors and function in older adults and patient populations.