Non-Axial Muscle Stress & Stiffness

横纹肌，无论是在肢体肌肉组织中还是在膈肌和心脏等肌肉器官中，都是由细长的活细胞组成的，这些活细胞被称为肌纤维。人们几乎总是假定，这种肌肉的功能是作为单轴力发生器，产生力并在纤维的方向上经历长度变化。除了极少数例外，肌肉力学的实验研究都集中在纤维方向上的收缩和力，所有当前的理论都假设，当嵌入大量收缩组织时，肌肉纤维的行为与单轴实验中测量的完全一致。但至少有一类实验——涉及渗透诱导的纤维横向扩张和压缩的实验——表明，可收缩组织的非轴向变形可以大大降低肌肉的力量。非轴向变形在正常生理功能中经常发生，目前尚无方法定量估计其对横纹肌产生的主动应力的影响。本研究的目的是发展非轴向肌肉变形效应的定量理论。提出的理论是对由英国生物物理学家A.F.赫胥黎首先提出的在分子水平上建立的肌肉收缩数学理论的概括。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的水平上产生重要的影响。在应用层面上，定量预测非轴向变形对活动肌肉应力的影响的能力将清楚地确定这些影响何时重要，何时不重要，并在运动、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——这些实验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. ***