The passive elastic modulus of muscle fiber appears to be size-dependent. The objectives of this study were to determine whether this size effect was evident in the mechanical testing of muscle fiber bundles and to examine whether the muscle fiber bundle cross-section is circular. Muscle fibers and fiber bundles were extracted from lumbar spine multifidus and longissimus of three cohorts: group one (G1) and two (G2) included 13 (330 ± 14 g) and 6 (452 ± 28 g) rats, while Group 3 (G3) comprised 9 degenerative spine patients. A minimum of six muscle fibers and six muscle fiber bundles from each muscle underwent cumulative stretches, each of 10% strain followed by 4 minutes relaxation. For all specimens, top and side diameters were measured. Elastic modulus was calculated as tangent at 30% strain from the stress–strain curve. Linear correlations between the sample cross sectional area (CSA) and elastic moduli in each group were performed. The correlations showed that increasing specimen CSA resulted in lower elastic modulus for both rats and humans, muscle fibers and fiber bundles. The median ratio of major to minor axis exceeded 1.0 for all groups, ranging between 1.15–1.29 for fibers and 1.27–1.44 for bundles. The lower elastic moduli with increasing size can be explained by relatively less collagenous extracellular matrix in the large fiber bundles. Future studies of passive property measurement should aim for consistent bundle sizes and measuring diameters of two orthogonal axes of the muscle specimens.

肌肉纤维的被动弹性模量似乎与尺寸有关。本研究的目的是确定这种尺寸效应在肌纤维束的力学测试中是否明显，并检查肌纤维束横截面是否为圆形。从三个队列的腰椎多裂肌和最长肌中提取肌肉纤维和纤维束：第一组 (G1) 和第二组 (G2) 包括 13 (330 ± 14 g) 和 6 (452 ± 28 g) 大鼠，而第三组 (G3) ) 包括 9 名退行性脊柱患者。至少 6 根肌肉纤维和来自每块肌肉的 6 根肌肉纤维束进行累积拉伸，每个拉伸 10%，然后放松 4 分钟。对于所有样品，测量了顶部和侧部直径。弹性模量计算为应力-应变曲线的 30% 应变处的切线。进行了每组样品横截面积 (CSA) 和弹性模量之间的线性相关性。相关性表明，增加样本 CSA 导致大鼠和人类、肌肉纤维和纤维束的弹性模量降低。所有组的长轴与短轴的中值比都超过 1.0，纤维的范围在 1.15-1.29 之间，束的范围在 1.27-1.44 之间。随着尺寸的增加，弹性模量越低，可以用大纤维束中相对较少的胶原细胞外基质来解释。被动特性测量的未来研究应旨在使肌肉标本的两个正交轴的束尺寸和测量直径一致。相关性表明，增加样本 CSA 导致大鼠和人类、肌肉纤维和纤维束的弹性模量降低。所有组的长轴与短轴的中值比都超过 1.0，纤维的范围在 1.15-1.29 之间，束的范围在 1.27-1.44 之间。随着尺寸的增加，弹性模量越低，可以用大纤维束中相对较少的胶原细胞外基质来解释。被动特性测量的未来研究应旨在使肌肉标本的两个正交轴的束尺寸和测量直径一致。相关性表明，增加样本 CSA 导致大鼠和人类、肌肉纤维和纤维束的弹性模量降低。所有组的长轴与短轴的中值比都超过 1.0，纤维的范围在 1.15-1.29 之间，束的范围在 1.27-1.44 之间。随着尺寸的增加，弹性模量越低，可以用大纤维束中相对较少的胶原细胞外基质来解释。被动特性测量的未来研究应旨在使肌肉标本的两个正交轴的束尺寸和测量直径一致。随着尺寸的增加，弹性模量越低，可以用大纤维束中相对较少的胶原细胞外基质来解释。被动特性测量的未来研究应旨在使肌肉标本的两个正交轴的束尺寸和测量直径一致。随着尺寸的增加，弹性模量越低，可以用大纤维束中相对较少的胶原细胞外基质来解释。被动特性测量的未来研究应旨在使肌肉标本的两个正交轴的束尺寸和测量直径一致。