Non-Axial Muscle Stress & Stiffness

9626736扎哈拉克横纹肌，无论是四肢肌肉组织，还是横隔膜和心脏等肌肉器官，都是由称为肌肉纤维的细长活细胞组成的。人们几乎总是认为，这种肌肉的功能是单轴力生成器，产生力，并经历纤维方向的长度变化。除了极少数例外，肌肉力学的实验研究一直集中在纤维方向的收缩和力上，所有现有的理论都假设，当肌肉纤维嵌入大量收缩组织中时，其行为与单轴实验中测得的完全相同。但至少有一类实验--那些涉及渗透诱导的横向纤维扩张和压缩的实验--表明，收缩组织的非轴向变形可以大大降低肌肉力量。目前尚无定量估计正常生理功能中常见的非轴向变形对横纹肌所产生的主动应力的影响的方法。本研究的目的是建立肌肉非轴向变形效应的定量理论。提出的理论是在分子水平上建立的肌肉收缩数学理论的推广，该理论首先由英国生物物理学家A.F.赫胥黎提出。这项工作的成功完成将在应用生物力学和基础生物物理学两个层面上产生重要影响。在应用水平上，定量预测非轴向变形对主动肌肉应力的影响的能力将清楚地识别这些影响何时重要、何时不重要的情况，并有助于在运动、运动控制、心脏力学、呼吸力学和相关问题的研究中改进对肌肉功能的描述。在基础生物物理学的层面上，这样的定量理论可能会提出一些非传统的实验--例如，那些涉及轴向剪切、横向剪切或扭转的实验--现在将提供关于肌肉收缩的基本分子机制的信息。***

9626736 Zahalak Striated muscle, whether found in the limb musculature or muscular organs like the diaphragm and the heart, is composed of thin elongated living cells called muscle fibers. It has been assumed, almost invariably, that such muscle functions as a uniaxial force generator, producing forces and experiences length changes in the direction of the fibers. With rare exceptions, experimental investigations of muscle mechanics have focused on contractions and forces in the fiber directions, and all current theories assume that when embedded in a mass of contractile tissue muscle fibers behave exactly as measured in uniaxial experiments. But at least one class of experiments--those involving osmotically-induced expansion and compression transverse to the fibers--suggest that non-axial deformations of contractile tissue can greatly reduce muscle force. At present there exists no method for estimating quantitatively the effects of non-axial deformations, which occur often in normal physiological function, on the active stresses generated by striated muscle. The goal of this research is to develop a quantitative theory of non-axial deformation effects in muscle. The proposed theory is a generalization of the well established mathematical theory of muscle contraction at the molecular level, first formulated by the English biophysicist, A.F. Huxley. Successful completion of this work will have important implications at both the levels of applied biomechanics and fundamental biophysics. At the applied level, an ability to predict quantitatively the effects of non- axial deformations on active muscle stress will clearly identify the circumstances when these effects are important and when they am not, and lead to improved descriptions of muscle function in studies of locomotion, motor control, cardiac mechanics, respiratory mechanics, and related problems. At the level of basic biophysics, such a quantitative theory may suggest some non- traditional exper iments--for example, those involving axial shear, transverse shear, or torsion--that will provide now information about the fundamental molecular mechanisms of muscle contraction. ***