In the deltoid muscles of Pan troglodytes and Homo sapiens, we have analyzed the muscle architecture and the expression of the myosin heavy chain (MHC) isoforms. Our aim was to identify differences between the two species that could be related to their different uses of the upper limb. The deltoid muscle of six adult Pan troglodytes and six adult Homo sapiens were dissected. The muscle fascicle length (MFL) and the physiological cross-sectional area (PCSA) of each muscle were calculated in absolute and normalized values. The expression pattern of the MHC-I, MHC-IIa and MHC-IIx isoforms was analyzed in the same muscles by real-time polymerase chain reaction. Only the acromial deltoid (AD) presented significant architectural differences between the two species, with higher MFL values in humans and higher PCSA values in chimpanzees. No significant differences in the expression pattern of the MHC isoforms were identified. The higher PCSA values in the AD of Pan troglodytes indicate a greater capacity of force generation in chimpanzees than in humans, which may be related to a greater use of the upper limb in locomotion, specifically in arboreal locomotion like vertical climbing. The functional differences between chimpanzees and humans in the deltoid muscle are more related to muscle architecture than to a differential expression of MHC isoforms.

中文翻译：

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黑猩猩 (Pan troglodytes) 和现代人类 (Homo sapiens) 三角肌的解剖学和分子分析：上肢使用的异同

在Pan troglodytes和Homo sapiens的三角肌中，我们分析了肌肉结构和肌球蛋白重链 (MHC) 同种型的表达。我们的目的是确定这两个物种之间的差异，这些差异可能与它们对上肢的不同用途有关。六名成年泛穴居人和六名成年智人的三角肌被解剖了。以绝对值和标准化值计算每块肌肉的肌肉束长度 (MFL) 和生理横截面积 (PCSA)。通过实时聚合酶链反应在相同肌肉中分析 MHC-I、MHC-IIa 和 MHC-IIx 同种型的表达模式。只有肩峰三角肌 (AD) 在两个物种之间呈现出显着的结构差异，人类的 MFL 值较高，黑猩猩的 PCSA 值较高。未发现 MHC 同种型的表达模式有显着差异。Pan troglodytes AD中较高的PCSA值表明黑猩猩比人类产生更大的力的能力，这可能与在运动中更多地使用上肢有关，特别是在垂直攀爬等树栖运动中。黑猩猩和人类在三角肌中的功能差异更多地与肌肉结构有关，而不是与 MHC 异构体​​的差异表达有关。