Aim: The present study aimed to simultaneously examine the age-related, muscle-specific, sex-specific and contractile-mode-specific changes in isolated mouse skeletal muscle function and morphology across multiple ages. Methods: Measurements of mammalian muscle morphology, isometric force and stress (force/cross-sectional area), absolute and normalised (power/muscle mass) work loop power across a range of contractile velocities, fatigue resistance, and myosin heavy chain (MHC) isoform concentration were measured in 232 isolated mouse (CD-1) soleus, extensor digitorum longus (EDL) and diaphragm from male and female individuals aged 3-, 10-, 30-, 52-, and 78-wks. Results: Ageing resulted in increased body mass, and soleus and EDL muscle mass, with atrophy only present for female EDL by 78-wks despite no change in MHC isoform concentration. Absolute force and power output increased up to 52-wks and to a higher level for males. A 23%-36% loss of isometric stress exceeded the 14%-27% loss of power normalised to muscle mass between 10-wks and 52-wks, though the loss of normalised power between 52-78-wks continued without further changes in stress (P>0.23). Males had lower power normalised to muscle mass than females by 78-wks, with the greatest decline observed for male soleus. Ageing did not cause a shift towards slower contractile characteristics, with reduced fatigue resistance observed in male EDL and female diaphragm. Conclusion: Our findings show that the loss of muscle quality precedes the loss of absolute performance as CD-1 mice age, with the greatest effect seen in male soleus, and in most instances without muscle atrophy or an alteration in MHC isoforms.

中文翻译：

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离体小鼠骨骼肌功能的年龄相关变化取决于性别，肌肉和收缩模式。

目的：本研究旨在同时检查多个年龄段的孤立小鼠骨骼肌功能和形态的年龄相关性，肌肉特异性，性别特异性和收缩模式特异性变化。方法：在一系列收缩速度，抗疲劳性和肌球蛋白重链（MHC）范围内测量哺乳动物的肌肉形态，等距力和应力（力/横截面积），绝对和归一化（功率/肌肉质量）工作循环功率在232、3、10、30、52和78周龄男性和女性个体的232只离体小鼠（CD-1）比目鱼，长指伸肌（EDL）和diaphragm肌中测量同工型浓度。结果：衰老导致体重，比目鱼肌和EDL肌肉增加，尽管MHC亚型浓度没有变化，但女性EDL萎缩仅78周。男性的绝对力量和功率输出增加到52周，并达到更高的水平。等轴测应力的23％-36％的损失超过了在10周至52周之间归一化为肌肉质量的14％-27％的力量损失，尽管52-78周之间的归一化力量继续消失，但应力（P> 0.23）。男性的正常肌肉力量比女性低78周，其中男性比目鱼的跌幅最大。老化并没有导致收缩特性的降低，而在男性EDL和女性隔膜中观察到的抗疲劳性降低。结论：我们的发现表明，随着CD-1小鼠年龄的增长，肌肉质量的丧失先于绝对性能的丧失，在男性比目鱼中效果最大，在大多数情况下，肌肉无萎缩或MHC亚型没有改变。