Muscle Energetics during Fatiguing Contractions in Young and Old Men

描述(申请人提供)：尽管老年人往往比年轻人更疲惫，但这并不是一个普遍的发现。正如国家老龄研究所(NIA)在一次关于老年人不明原因疲劳的探索性研讨会中提出的那样，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。我们建议比较青年男性和老年男性在两种类型的肘屈肌疲劳收缩时，协同肌、拮抗肌和附属肌之间的激活和能量利用的分布。这两种收缩的区别在于手臂肌肉支持的负荷类型：一种疲劳性收缩需要个体维持次最大力量(力量任务)，而另一种疲劳性收缩将涉及支持等量的惯性负载并保持手臂位置不变(位置任务)。虽然在两次收缩中施加的净肌肉扭矩对于每个受试者来说都是相似的，但姿势任务更难，不能像力量任务那样持续很长时间。研究计划的中心假设是，在两个任务中，手臂和附属肌肉的能量学差异可以解释任务失败时间上与年龄相关的差异。正电子发射断层扫描(PET)将与计算机断层扫描(CT)相结合，在力量和姿势任务中测量手臂肌肉的血流量和氧气消耗，PET图像将提供有关个别肌肉葡萄糖摄取的信息，以估计肌肉活动的累积水平。该研究计划首先比较老年人和年轻人在两种疲劳性收缩时手臂肌肉的血流量和耗氧量(目标1)，然后比较老年人和年轻人在两种疲劳性收缩后手臂和附属肌肉的葡萄糖摄取量(目标2)。尽管年轻人和老年人在体位任务中的相对表现尚不清楚，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，可以开发特定的干预措施来最大限度地提高老年人的疲劳抵抗力。 公共卫生相关性：年轻人和老年人会表现出两种不同难度的疲劳性收缩。该计划是为了确定两组参与者之间的表现差异是否可以用相关肌肉的血流和能量消耗的差异来解释。

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.