Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, ON N1G 2W1, Canada.
Sports Medicine, Health and Performance Centre, University of Guelph, Guelph, ON N1G 2W1, Canada.
J Biomech Eng. 2020 Aug 1;142(8). doi: 10.1115/1.4047423.
Studies on single muscle fiber passive material properties often report relatively large variation in elastic modulus (or normalized stiffness), and it is not clear where this variation arises. This study was designed to determine if the stiffness, normalized to both fiber cross-sectional area and length, is inherently different between types 1 and 2 muscle fibers. Vastus lateralis fibers (n = 93), from ten young men, were mechanically tested using a cumulative stretch-relaxation protocol. SDS-PAGE classified fibers as types 1 or 2. While there was a difference in normalized stiffness between fiber types (p = 0.0019), an unexpected inverse relationship was found between fiber diameter and normalized stiffness (r = -0.64; p < 0.001). As fiber type and diameter are not independent, a one-way analysis of covariance (ANCOVA) including fiber diameter as a covariate was run; this eliminated the effect of fiber type on normalized stiffness (p = 0.1935). To further explore the relationship between fiber size and elastic properties, we tested whether stiffness was linearly related to fiber cross-sectional area, as would be expected for a homogenous material. Passive stiffness was not linearly related to fiber area (p < 0.001), which can occur if single muscle fibers are better represented as composite materials. The rule of mixtures for composite materials was used to explore whether the presence of a stiff perimeter-based fiber component could explain the observed results. The model (R2 = 0.38) predicted a perimeter-based normalized stiffness of 8800 ± 2600 kPa/μm, which is within the range of basement membrane moduli reported in the literature.
研究单根肌纤维的被动力学特性时，常发现弹性模量（或归一化刚度）存在较大变异，但其变异来源并不明确。本研究旨在确定 1 型和 2 型肌纤维的固有刚度（与纤维横截面积和长度归一化后的值）是否存在差异。从 10 名年轻男性的股外侧肌中分离纤维（n=93），并采用累积拉伸-松弛方案进行机械测试。SDS-PAGE 将纤维分为 1 型或 2 型。尽管纤维类型间的归一化刚度存在差异（p=0.0019），但出人意料的是，纤维直径与归一化刚度呈负相关（r=-0.64；p<0.001）。由于纤维类型和直径并非相互独立，因此进行了包含纤维直径作为协变量的单向方差分析（ANCOVA）；这消除了纤维类型对归一化刚度的影响（p=0.1935）。为了进一步探讨纤维大小与弹性特性之间的关系，我们检验了刚度是否与纤维横截面积呈线性关系，这是同质材料的预期表现。被动刚度与纤维面积无明显线性关系（p<0.001），这可能是由于单根肌纤维更类似于复合材料。我们使用复合材料混合物法则来探究是否存在基于硬边的纤维成分能够解释观察到的结果。该模型（R2=0.38）预测基于硬边的归一化刚度为 8800±2600kPa/μm，这与文献中报道的基膜模量范围一致。
