Neuromechanics of Differential Motor Unit Activation in Multifunctional Muscles

描述（由申请人提供）：肌肉中运动单位的募集通常被理解为以固定的顺序从施加小力的单位进展到施加大力的单位。然而，这种理解在文献中受到质疑，因为研究表明，某些肌肉中的运动单位在关节力的不同方向上被不同地招募。然而，运动单位的差异激活的生理基础尚未建立。使用第一背侧骨间肌（FDI）作为模型多功能肌肉，我们将确定FDI内的不同运动单元是否以不同的外展屈曲力比施加抽搐力。如果不同的运动单位在一个方向上比另一个方向有更大的机械优势，我们将确定中枢神经系统（CMS）是否激活了运动单位，以便优先激活给定任务中具有最大机械优势的单位。中风后患手方向控制的丧失可能与运动单位的选择性激活故障有关，从而使食指力的某些方向无法接近或无法控制。我们的研究将确定这一假设的可行性，寻求建立在未受损的人类受试者的差异运动单位激活的生理基础。我们将使用尖峰触发平均法（STA）来评估运动单位的抽搐力方向. STA可以准确地确定运动单元抽搐力方向，尽管它不能准确地估计抽搐的绝对幅度。我们将检查跨不同方向任务的抽搐方向的STA估计的一致性。通过研究许多运动单位，我们将评估由FDI运动单位产生的抽搐方向的分布。我们将确定运动单位的抽搐方向与其募集之间是否存在相关性。我们的研究将确定STA是否是一个可靠的指标，运动单位抽搐力的方向，并确定是否不同的抽搐力方向之间的运动单位形成的生理基础，差异运动单位激活。与公共卫生的相关性：中风后，许多人失去了在特定方向移动关节的能力。我们的研究旨在开发方法来检查脊髓中单个细胞控制的运动方向，并确定未受损的大脑如何激活这些细胞来控制关节运动的不同方向。有了这些信息将为我们提供一个基线，然后我们可以使用它来更好地了解受损的大脑如何控制脊髓，以及特定的干预措施如何改善中风后的运动控制。

DESCRIPTION (provided by applicant): The recruitment of motor units in a muscle is generally understood to progress in a fixed order from units that exert small forces to units that exert large forces. However, this understanding has been questioned in the literature as studies have shown that motor units in some muscles are recruited differently for different directions of joint force. However, the physiological basis for the differential activation of motor units has not been established. Using the first dorsal interosseous (FDI) as a model multifunctional muscle, we will determine if different motor units within the FDI exert twitch forces with different ratios of abduction to flexion force. If different motor units have a greater mechanical advantage for one direction over another, we will determine if the central nervous system (CMS) activates motor units so that units with the greatest mechanical advantage for the given task are preferentially activated. Loss of directional control in the affected hand after stroke may relate to a breakdown in the selective activation of motor units rendering some directions of index finger force either inaccessible or uncontrollable. Our study will determine the feasibility of this hypothesis by seeking to establish the physiological basis of differential motor unit activation in unimpaired human subjects. We will assess motor unit twitch force direction using spike- triggered averaging (STA). STA may accurately determine motor unit twitch force direction despite the fact that it can not accurately estimate the absolute amplitude of a twitch. We will examine the consistency of STA estimates for twitch direction across different directional tasks. By studying many motor units, we will assess the distribution of twitch directions that can be generated by FDI motor units. We will determine if a correlation exists between the twitch direction of a motor unit and its recruitment. Our study will both determine whether STA is a reliable indicator of motor unit twitch force direction, and determine whether different twitch force directions among motor units forms the physiological basis for differential motor unit activation. Relevance to Public Health: After suffering a stroke, many individuals lose the ability to move their joints in particular directions. Our study seeks both to develop methods to examine the direction of movement controlled by single cells in the spinal cord, and to determine how the undamaged brain activates these cells to control different directions of joint movement. Having this information will give us a baseline which we can then use to better understand how the damaged brain controls the spinal cord, and how specific interventions may improve motor control post-stroke.