Task Dependence of Muscle Fatigue in Older Adults

描述（由申请人提供）：NIA试点研究计划，主题14：感觉和运动处理肌肉的耐力将随着执行的任务而变化。然而，在老年人中，神经肌肉系统内与年龄相关的变化对肌肉疲劳的任务依赖性的影响尚未探讨。这就提出了以下问题：年龄是否会改变神经肌肉系统适应不同疲劳任务的能力？在年轻成人中，与维持恒定肘角同时在腕部支撑等效惯性负荷（位置任务）相比，维持力并推压力传感器（力任务）时进行次最大等长收缩时的耐受时间更长（Hunter等人，2002）。较短的耐力时间的位置任务是由于神经机制，包括更大的速度下降驱动器。考虑到神经肌肉系统中与年龄相关的变化会使老年人在疲劳任务期间易患神经系统损伤，本RO3应用程序检查了以下假设：由于神经机制中与年龄相关的损伤，与年轻人相比，老年人与力量任务相比，位置任务的次最大疲劳收缩的耐受时间差异更大。有三个具体目标来检验这一假设。第一个目标将比较的耐力时间和肌肉激活模式手肘屈肌在年轻人和老年人的位置任务和力量任务。目的2和3将评估潜在的机制与年龄相关的差异，在肌肉疲劳的两个任务，通过测量指标的下降驱动和外周传入反馈的肌肉在疲劳收缩。这些测量包括肌肉交感神经活动、心率、运动输出的波动、努力感和升压反应。本申请提出了一种新的方法来检查老年人的肌肉疲劳。研究结果将提供初步信息的类型的负载和支持的老年人在日常工作中的长期次最大的任务。这将为老年人肌肉疲劳的任务依赖性提供新的信息。这些初步发现将为RO 1应用奠定基础，该应用将进一步探索老年人肌肉疲劳的机制和任务依赖性。

DESCRIPTION (provided by applicant): NIA Pilot Research Program, Topic 14: Sensory and Motor Processing The endurance capacity of a muscle will vary with the task performed. However, the influence of age-related changes within the neuromuscular system on the task-dependent nature of muscle fatigue is unexplored in older adults. This raises the following question: Does age alter the ability of the neuromuscular system to adapt to different fatiguing tasks? In young adults, the endurance time when performing a submaximal isometric contraction was longer when maintaining a force and pushing against a force transducer (force task) compared with maintaining a constant elbow angle while supporting an equivalent inertial load at the wrist (position task) (Hunter et al. 2002). The briefer endurance time for the position task was attributable to neural mechanisms including a greater rate of descending drive. Given that age-related changes in the neuromuscular system will predispose the older adult to impairment within the nervous system during a fatiguing task, this RO3 application examines the following hypothesis: the difference in endurance time of a submaximal fatiguing contraction for a position task compared with a force task, will be greater in older adults compared with young adults due to age-related impairment in neural mechanisms. There are three specific aims to test this hypothesis. The first aim will compare the endurance time and muscle activation patterns of the elbow flexor muscles in young and older adults for a position task and force task. Aims 2 and 3 will evaluate potential mechanisms for the age-related differences in muscle fatigue of the two tasks, by measuring indices of descending drive and peripheral afferent feedback from the muscle during the fatiguing contractions. These measures include muscle sympathetic nerve activity, heart rate, fluctuations in motor Output, sense of effort and the pressor response. This application proposes a novel approach to examine muscle fatigue in older adults. The findings will provide preliminary information on the type of load and support preferred by older adults for long-duration submaximal tasks during daily tasks. This will constitute new information on the task-dependent nature of muscle fatigue in older adults. These preliminary findings will form the foundation for an RO 1 application that will further explore the mechanisms and task dependency of muscle fatigue in older adults.