Applied Physiology, Nutrition, and Metabolism, Ahead of Print.
Constitutional thinness (CT) is a nonpathological state of underweight. The current study aimed to explore skeletal muscle energy storage in individuals with CT and to further characterize muscle phenotype at baseline and in response to overfeeding. Thirty subjects with CT (15 females, 15 males) and 31 normal-weight control subjects (16 females, 15 males) participated in the study. Histological and enzymological analyses were performed on muscle biopsy specimens before and after overfeeding. In the skeletal muscle of CT participants compared with controls, we observed a lower content of intramuscular triglycerides for type I (−17%, p < 0.01) and type IIA (−14%, p < 0.05) muscle fibers, a lower glycogen content for type I (−6%, p < 0.01) and type IIA (−5%, p < 0.05) muscle fibers, a specific fiber-type distribution, a marked muscle hypotrophy (−20%, p < 0.001), a low capillary-to-fiber ratio (−19%, p < 0.001), and low citrate synthase activity (−18%, p < 0.05). In response to overfeeding, CT participants increased their intramuscular triglycerides content in type I (+10%, p < 0.01) and type IIA (+9%, p < 0.01) muscle fibers. CT individuals seem to present an unusual muscle phenotype and different adaptations to overfeeding compared with normal-weight individuals, suggesting a specific energy metabolism and muscle adaptations. ClinicalTrials.gov registration no. NCT02004821. Novelty Low intramuscular triglycerides and glycogen content in skeletal muscle of constitutionally thin individuals. Low oxidative capacity, low capillary supply, and fiber hypotrophy in skeletal muscle of constitutionally thin individuals. Increase in intramuscular triglycerides in constitutional thinness in response to overfeeding.

中文翻译：

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具有体质瘦弱的女性和男性的骨骼肌：低肌内脂质含量和氧化特征。

应用生理学、营养学和代谢，提前出版。
体质性消瘦 (CT) 是体重过轻的非病理状态。目前的研究旨在探索 CT 患者的骨骼肌能量储存，并进一步表征基线和过度喂养时的肌肉表型。30 名 CT 受试者（15 名女性，15 名男性）和 31 名正常体重对照受试者（16 名女性，15 名男性）参与了这项研究。在过度喂养之前和之后对肌肉活检标本进行组织学和酶学分析。与对照组相比，在 CT 参与者的骨骼肌中，我们观察到 I 型（-17%，p < 0.01）和 IIA 型（-14%，p < 0.05）肌纤维的肌内甘油三酯含量较低，糖原含量较低对于 I 型 (-6%, p < 0.01) 和 IIA 型 (-5%, p < 0.05) 肌纤维，特定的纤维类型分布，显着的肌肉萎缩 (-20%, p < 0.001)、低毛细血管纤维比 (-19%, p < 0.001) 和低柠檬酸合酶活性 (-18%, p < 0.05)。为了应对过度喂养，CT 参与者增加了 I 型（+10%，p < 0.01）和 IIA 型（+9%，p < 0.01）肌纤维的肌内甘油三酯含量。与体重正常的个体相比，CT 个体似乎呈现出不寻常的肌肉表型和对过度喂养的不同适应，这表明特定的能量代谢和肌肉适应。ClinicalTrials.gov 注册号 NCT02004821。新奇 体质瘦弱个体骨骼肌中肌内甘油三酯和糖原含量低。体质较瘦的个体骨骼肌氧化能力低、毛细血管供应低和纤维萎缩。