Klotz Thomas, Bleiler Christian, Röhrle Oliver
Chair for Continuum Biomechanics and Mechanobiology, Institute for Modelling and Simulation of Biomechanical Systems, University of Stuttgart, Stuttgart, Germany.
Stuttgart Center for Simulation Sciences (SC SimTech), University of Stuttgart, Stuttgart, Germany.
Front Physiol. 2021 Aug 2;12:685531. doi: 10.3389/fphys.2021.685531. eCollection 2021.
The well-established sliding filament and cross-bridge theory explain the major biophysical mechanism responsible for a skeletal muscle's active behavior on a cellular level. However, the biomechanical function of skeletal muscles on the tissue scale, which is caused by the complex interplay of muscle fibers and extracellular connective tissue, is much less understood. Mathematical models provide one possibility to investigate physiological hypotheses. Continuum-mechanical models have hereby proven themselves to be very suitable to study the biomechanical behavior of whole muscles or entire limbs. Existing continuum-mechanical skeletal muscle models use either an active-stress or an active-strain approach to phenomenologically describe the mechanical behavior of active contractions. While any macroscopic constitutive model can be judged by it's ability to accurately replicate experimental data, the evaluation of muscle-specific material descriptions is difficult as suitable data is, unfortunately, currently not available. Thus, the discussions become more philosophical rather than following rigid methodological criteria. Within this work, we provide a extensive discussion on the underlying modeling assumptions of both the active-stress and the active-strain approach in the context of existing hypotheses of skeletal muscle physiology. We conclude that the active-stress approach resolves an idealized tissue transmitting active stresses through an independent pathway. In contrast, the active-strain approach reflects an idealized tissue employing an indirect, coupled pathway for active stress transmission. Finally the physiological hypothesis that skeletal muscles exhibit redundant pathways of intramuscular stress transmission represents the basis for considering a mixed-active-stress-active-strain constitutive framework.
成熟的滑动丝和横桥理论解释了骨骼肌在细胞水平上主动行为的主要生物物理机制。然而，骨骼肌在组织尺度上的生物力学功能，这是由肌纤维和细胞外结缔组织的复杂相互作用引起的，却鲜为人知。数学模型为研究生理假设提供了一种可能性。连续介质力学模型已证明自身非常适合研究整块肌肉或整个肢体的生物力学行为。现有的连续介质力学骨骼肌模型要么采用主动应力方法，要么采用主动应变方法，从现象学角度描述主动收缩的力学行为。虽然任何宏观本构模型都可以通过其准确复制实验数据的能力来判断，但由于不幸的是目前没有合适的数据，对肌肉特定材料描述的评估很困难。因此，讨论变得更具哲学性，而不是遵循严格的方法论标准。在这项工作中，我们在骨骼肌生理学现有假设的背景下，对主动应力和主动应变方法的潜在建模假设进行了广泛讨论。我们得出结论，主动应力方法解决了一个理想化的组织通过独立途径传递主动应力的问题。相比之下，主动应变方法反映了一个理想化的组织采用间接耦合途径进行主动应力传递。最后，骨骼肌表现出肌肉内应力传递冗余途径的生理假设代表了考虑混合主动应力 - 主动应变本构框架的基础。
