MECHANICAL INTERACTIONS OF MOTOR UNITS

整个肌肉-肌腱复合体的力学模型通常假设 单独的肌肉纤维-肌腱纤维单位独立起作用。只有几个人 例外的是，以前对肌肉功能的实验分析 基于对单个离体肌纤维的研究，单个肌纤维的激活 运动单位或肌肉的所有运动单位的激活。然而， 在生理条件下，肌肉力量通过招募来分级。 可变数量的电机单元和调制这些单元的点火速率 机动装置。肌肉产生的总力不仅取决于 电机单元的固有属性还取决于机械 运动单元之间的相互作用。事实上，重要的机械连接 独立电机单元之间的连接可能既产生于 肌腱股，它们的纤维插入和来自连接 相邻肌肉纤维之间的组织连接。这项研究的目的 在本申请中提出的项目是量化机械 单个肌肉内运动单位之间的相互作用和探索 这些相互作用的机制。 电机单元之间的两种类型的机械相互作用 如前所述：(1)单个电机单元的非线性求和 紧张，其中由同时启动的单元产生的紧张是 大于它们各自张力的线性总和，以及(2)“力-- 协助“，其中由马达单元产生的张力被增强 在叠加了另一个单元的激活和停用之后。 前一种效应归因于摩擦力的减少。 在主动和被动肌肉纤维之间，而后一种效应可能 取决于由电机单元激活产生的内部长度变化。 拟议中的实验的具体目的是进一步调查 非线性求和与寻址助力现象 以下问题： 1.主动和主动之间的内耗的来源和性质是什么 被动肌肉纤维？ 2.是否由于内部长度变化而导致的强制协助 启动马达装置？ 3.非线性力和力的大小是多少？ 与激活的运动单位的数量、肌腱顺应性、 运动单位类型和肌肉结构？

Mechanical models of whole muscle-tendon complexes often assume that individual muscle fiber-tendon fiber units act independently. With few exceptions, previous experimental analyses of muscle function have been based on studies of single isolated muscle fibers, activation of single motor units or activation of all the motor units of a muscle. However, under physiological conditions, muscle force is graded by recruiting variable numbers of motor units and modulating the firing rate of those motor units. The total force produced by the muscle depends not only on the intrinsic properties of the motor units but also upon mechanical interactions between motor units. In fact, significant mechanical linkages between separate motor units may arise both from links between the tendinous strands into which their fibers insert and from connective tissue links between adjacent muscle fibers. The goal of the research projects proposed in this application is to quantify the mechanical interactions between the motor units within a single muscle and to explore the mechanisms of these interactions. Two types of mechanical interactions between motor units have been previously described: (1) nonlinear summation of individual motor unit tensions, where the tension produced by concurrently activated units is greater than the linear sum of their individual tensions, and (2) "force- assistance", where the tension produced by a motor unit is enhanced following the superimposed activation and deactivation of another unit. The former effect has been attributed to a reduction of frictional forces between active and passive muscle fibers, while the latter effect may depend upon the internal length changes produced by motor unit activation. The specific aims of the proposed experiments are to further investigate the phenomena of nonlinear summation and force assistance by addressing the following questions: 1. What is the source and nature of internal friction between active and passive muscle fibers? 2. Is force assistance due to internal length changes produced by activation of motor units? 3. How are the magnitudes of nonlinear force summation and force assistance related to numbers of motor units activated, tendon compliance, motor unit type and muscle architecture?