Department of Biomedical Sciences, University of Padova, Padova, Italy.
Biomed Res Int. 2013;2013:249398. doi: 10.1155/2013/249398. Epub 2013 Jul 22.
The aim of our study was to investigate fiber type distribution and contractile characteristics of Latissimus Dorsi muscle (LDM). Samples were collected from 18 young healthy subjects (9 males and 9 females) through percutaneous fine needle muscle biopsy. The results showed a predominance of fast myosin heavy chain isoforms (MyHC) with 42% of MyHC 2A and 25% of MyHC 2X, while MyHC 1 represented only 33%. The unbalance toward fast isoforms was even greater in males (71%) than in females (64%). Fiber type distribution partially reflected MyHC isoform distribution with 28% type 1/slow fibers and 5% hybrid 1/2A fibers, while fast fibers were divided into 30% type 2A, 31% type A/X, 4% type X, and 2% type 1/2X. Type 1/slow fibers were not only less abundant but also smaller in cross-sectional area than fast fibers. During maximal isometric contraction, type 1/slow fibers developed force and tension significantly lower than the two major groups of fast fibers. In conclusion, the predominance of fast fibers and their greater size and strength compared to slow fibers reveal that LDM is a muscle specialized mainly in phasic and powerful activity. Importantly, such specialization is more pronounced in males than in females.
本研究旨在探讨 Latissimus Dorsi 肌肉（LDM）的纤维类型分布和收缩特性。通过经皮细针肌肉活检，从 18 名年轻健康受试者（9 名男性和 9 名女性）中采集样本。结果显示，快肌肌球蛋白重链同工型（MyHC）占主导地位，其中 MyHC 2A 占 42%，MyHC 2X 占 25%，而 MyHC 1 仅占 33%。男性（71%）快型同工型的不平衡程度甚至高于女性（64%）。纤维类型分布部分反映了 MyHC 同工型分布，其中 1/慢纤维占 28%，1/2A 混合纤维占 5%，而快纤维分为 2A 型 30%、A/X 型 31%、X 型 4%和 1/2X 型 2%。1/慢纤维不仅数量较少，而且横截面积也小于快纤维。在最大等长收缩时，1/慢纤维产生的力和张力明显低于两种主要快纤维群。总之，快纤维的优势及其与慢纤维相比更大的尺寸和强度表明，Latissimus Dorsi 肌肉主要专门用于相位和有力的活动。重要的是，这种专业化在男性中比在女性中更为明显。
