Telley I A, Denoth J, Ranatunga K W
Muscle Mechanics Group, Laboratory for Biomechanics, ETH Zurich, Schlieren CH-8952, Switzerland.
Adv Exp Med Biol. 2003;538:481-500; discussion 500. doi: 10.1007/978-1-4419-9029-7_44.
The sarcomere is the functional unit of muscle, and all sarcomeres are connected in series in myofibrils within a muscle fibre. From this point of view of the structure a single model consisting of a contractile, a series and a parallel element can not account for the description of a real muscle fibre. Additionally, the titin protein filament needs to be considered as a passive visco-elastic element in parallel with the contractile apparatus. Therefore, the structure of a single muscle fibre is complex due mechanical elements ("motors") operating in series and in parallel. Moreover, variability does exist in the mechanical properties along a fibre and hence a multi-segmental model is more realistic and would give rise to many new insights. By attributing a segment model to each half-sarcomere, a fibre can be constructed through rigorous coupling of these units in series and parallel. The dynamics of such a multi-segmental model is much more complex, but it can explain a variety of effects reported in standard classical mechanics experiments. With a relatively simple mechanistic description we can show that the dynamics of such multi-sarcomere systems exhibit a variety of effects (relaxation phenomena, permanent extra-tension, biphasic force-velocity relation) and should therefore not be neglected in muscle fibre modelling. We have observed in single skinned fibre experiments that non-uniformities in sarcomere length changes are prominent during activation and relaxation.
肌节是肌肉的功能单位，所有肌节在肌纤维内的肌原纤维中串联相连。从这种结构角度来看，由一个收缩元件、一个串联元件和一个并联元件组成的单一模型无法解释真实肌纤维的情况。此外，肌联蛋白丝需要被视为与收缩装置并联的被动粘弹性元件。因此，由于机械元件（“马达”）串联和并联运行，单个肌纤维的结构很复杂。而且，沿着纤维的力学性能存在变异性，因此多节段模型更现实，会带来许多新的见解。通过为每个半肌节赋予一个节段模型，可以通过将这些单元进行严格的串联和并联耦合来构建纤维。这种多节段模型的动力学要复杂得多，但它可以解释标准经典力学实验中报道的各种效应。通过相对简单的机械描述，我们可以表明这种多肌节系统的动力学表现出各种效应（松弛现象、永久性额外张力、双相力 - 速度关系），因此在肌纤维建模中不应被忽视。我们在单根去表皮纤维实验中观察到，在激活和松弛过程中，肌节长度变化的不均匀性很明显。
