Muscle Energetics during Fatiguing Contractions in Young and Old Men

描述（由申请人提供）：虽然老年人通常比年轻人更容易疲劳，但这并不是一个普遍的发现。正如美国国家老龄化研究所（NIA）关于老年人不明原因疲劳的探索性研讨会所提出的那样，年轻人和老年人之间的这种表现差异可能与肌肉能量学有关。我们建议比较年轻人和老年人在肘关节屈肌两种疲劳收缩时，一组协同肌、拮抗肌和副肌的激活分布和能量利用。两种收缩之间的区别在于手臂肌肉所承受的负荷类型：一种疲劳收缩需要个体承受次最大的力（力任务），另一种疲劳收缩需要支撑等效的惯性负荷并保持手臂的位置不变（位置任务）。虽然每个受试者在两次收缩过程中所施加的净肌肉扭矩相似，但位置任务难度更大，不能像力任务那样持续时间长。该研究计划的核心假设是，在两种任务中，手臂和附属肌肉的能量学差异可以解释任务失败时间的年龄相关差异。正电子发射断层扫描（PET）将与计算机断层扫描（CT）相结合，测量力量和位置任务时手臂肌肉的血流量和耗氧量，PET图像将提供单个肌肉的葡萄糖摄取信息，以估计肌肉活动的累积水平。研究计划首先比较老年和青年男性在两种类型的疲劳收缩时手臂肌肉的血流量和耗氧量（Aim 1），然后比较老年和青年男性在两种类型的疲劳收缩后手臂和附属肌肉的葡萄糖摄取（Aim 2）。虽然年轻人和老年人在位置任务中的相对表现是未知的，但我们希望通过肌肉能量学的差异来解释两种任务在失败时间上的差异。通过了解肌肉能量学的任务依赖作用，可以制定具体的干预措施，以最大限度地提高老年人的疲劳抵抗力。

DESCRIPTION (provided by applicant): Although old adults are often more fatigable than young adults, this is not a universal finding. As suggested in an exploratory workshop by the National Institute of Aging (NIA) on unexplained fatigue in the elderly, such differences in performance between young and old adults may be related to muscle energetics. We propose to compare the distribution of activation and energy utilization among a group of synergist, antagonist, and accessory muscles in young and old men during two types of fatiguing contractions with the elbow flexor muscles. The difference between the two contractions will be the type of load supported by the arm muscles: one fatiguing contraction will require an individual to sustain a submaximal force (force task) and the other fatiguing contraction will involve supporting an equivalent inertial load and keeping the position of the arm constant (position task). Although the net muscle torque exerted during the two contractions will be similar for each subject, the position task is more difficult and cannot be sustained for as long as the force task. The central hypothesis of the research plan is that differences in energetics of arm and accessory muscles during the two tasks can explain the age-related differences in times to task failure. Positron emission tomography (PET) will be combined with computer tomography (CT) to measure blood flow and oxygen consumption in arm muscles during force and position tasks, and PET images will provide information about the glucose uptake in individual muscles to estimate cumulative levels of muscle activity. The research plan involves first comparing blood flow and oxygen consumption in arm muscles of old and young men during two types of fatiguing contractions (Aim 1) and then comparing glucose uptake in arm and accessory muscles of old and young men after two types of fatiguing contractions (Aim 2). Although the relative performance of young and old men during a position task is unknown, we expect to explain any differences in time to failure for both tasks by differences in muscle energetics. By understanding the task dependent role of muscle energetics, specific interventions can be developed to maximize fatigue resistance in older adults. Public Health Relevance: Young and old men will perform two types of fatiguing contractions that differ in difficulty. The plan is to determine if differences in performance between the two groups of participants can be explained by variation in blood flow and energy consumption in the involved muscles.