Neuromuscular Fatigue in Older Adults

描述(由申请者提供)：这份申请调查了与日常活动功能更相关的任务中与年龄相关的神经肌肉疲劳的原因，这些任务对于在美国老龄化人口中保持老年人的独立性很重要。这一建议为了解老年人神经肌肉系统的疲劳性提供了一种新的创新方法，通过检查与功能相关的任务，这些任务需要在有限的肢体支持下控制负荷，并为动态任务保持力量。最近的研究表明，在这些与功能更相关的任务中，老年人比年轻人经历更大的肌肉疲劳。然而，老年人在肢体支持有限的次极量动态和姿势收缩时，与年龄相关的肌肉疲劳增加的原因尚不清楚。根据初步数据，我们假设，与年轻人相比，老年人表现出更大的疲劳是神经机制导致需要支持惯性负荷的次极量疲劳收缩。首先，我们研究了动态和姿势任务中肌肉疲劳的年龄相关变化的机制，这些任务涉及支持惯性负荷。具体地说，我们将比较年轻人和老年人在姿势等长和动态任务中失败的时间，并建立老年人年龄相关性疲劳和功能能力之间的联系(目标1)。我们还将确定导致年轻人和老年人在这些任务中失败的时间的神经机制(目标2)。为了实现目标2，我们将使用经颅磁刺激来检测疲劳前、疲劳中和疲劳后皮质脊髓的兴奋性，并将其量化为与神经肌肉传播(M波)变化归一化的运动诱发电位的大小。通过了解在与功能相关的任务中导致年龄相关性疲劳的程度和机制，我们可以找到适当和简单的康复技术来改善老年人所经历的日益严重的疲劳。我们的初步数据表明，“练习”疲惫的任务将通过神经适应来提高表现。因此，我们将通过练习年轻人和老年人进行的姿势等长和动态任务来确定任务失败时间和皮质脊髓兴奋性的变化(目标3)。这最后一个目标将评估“练习”作为一种康复技术的有效性，以改善老年人的神经肌肉功能缺陷并将损伤降至最低，并提供与年龄相关的神经功能损害的证据。

DESCRIPTION (provided by applicant): This application examines the cause for age-associated neuromuscular fatigue in tasks that are more functionally relevant to daily activities and that are important for maintenance of independence in old adults within an aging American population. This proposal brings a new and innovative approach to understanding fatigability of the neuromuscular system in old adults by examining functionally relevant tasks that require control of a load with limited limb support and maintenance of power for a dynamic task. Recent studies indicate that older adults experience greater muscle fatigue than young adults during these more functionally relevant tasks. However, the causes of the increase in age-related muscle fatigue in old adults during submaximal dynamic and postural contractions with limited limb support are not understood. Based on preliminary data we hypothesize that neural mechanisms are responsible for greater fatigue exhibited by old adults compared with young adults for submaximal fatiguing contractions that require supporting an inertial load. First, we examine the mechanisms for age-related changes in muscle fatigue of dynamic and postural tasks that involve supporting an inertial load. Specifically, we will compare the time to task failure between young and old adults for a postural isometric and dynamic task and establish the association between the age-related fatigue and functional ability in old adults (Aim 1). We will also determine neural mechanisms that contribute to time to task failure for these tasks in young and old adults (Aim 2). To accomplish Aim 2, we will use transcranial magnetic stimulation to examine corticospinal excitability before, during and after fatigue and this will be quantified as the size of the motor evoked potential normalized to the changes in neuromuscular propagation (M wave). By understanding the magnitude and mechanisms that contribute to age-related fatigue during functionally relevant tasks, we can identify appropriate and simple rehabilitative techniques to improve the increased fatigue experienced by old adults. Our preliminary data suggests that 'practice' of a fatiguing task will improve performance via neural adaptations. Therefore, we will determine the change in time to task failure and corticospinal excitability with practice of a postural isometric and dynamic task performed by young and old adults (Aim 3). This last aim will evaluate the efficacy of 'practice' as a rehabilitative technique, to ameliorate neuromuscular function deficits and minimize impairments in old adults, and also to provide evidence of age-related neural impairments in performance.