MECHANICAL INTERACTIONS OF MOTOR UNITS

整个肌肉-肌腱复合体的力学模型通常假设， 单个肌纤维-腱纤维单位独立地起作用。除了少数 除此之外，以前对肌肉功能的实验分析一直是 基于对单个分离的肌纤维的研究，激活单个 运动单位或肌肉的所有运动单位的激活。然而，在这方面， 在生理条件下，肌肉力量的分级是通过招募 可变数量的运动单元， 运动单位肌肉产生的总力量不仅取决于 电动机单元的固有特性， 运动单位之间的相互作用。事实上，重要的机械连接 在单独的马达单元之间的连接可以由在马达单元之间的连接引起， 它们的纤维插入的腱股，从药隔 相邻肌纤维之间的组织连接。研究的目标 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， 这些相互作用的机制。 运动单元之间的两种类型的机械相互作用已经被研究。 如前所述：（1）单个运动单元的非线性求和 张力，其中由同时激活的单元产生的张力是 大于它们各自张力的线性和，以及（2）“力- 辅助”，其中由马达单元产生的张力被增强 在另一个单元的叠加激活和去激活之后。 前一种效应归因于摩擦力的减小 主动和被动肌纤维之间，而后者的效果可能 取决于由运动单元激活产生的内部长度变化。 拟议实验的具体目的是进一步研究 非线性求和和力辅助现象 以下问题： 1.积极与消极之间的内部摩擦的来源和性质是什么？ 被动肌肉纤维？ 2.力辅助是由于内部长度变化产生的， 激活运动单位 3.非线性力和力的大小 与激活的运动单位数量，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?