The ratio between muscle strength and muscle cross-sectional area is called the specific force. Fatty replacement of muscles is seen in many myopathies, affecting the specific force, without necessarily affecting the ability of the remaining muscle fibers to contract. This ability is called the contractility and is the ratio between muscle strength and the lean muscle cross-sectional area, i.e. the contractile cross-sectional area. We hypothesized that contractility is disrupted in patients with congenital myopathy, because of defects in contractile proteins of the sarcomere. Peak torque across ankle and knee joints was measured by isokinetic dynamometry in 16 patients with congenital myopathy and 13 healthy controls. Five patients only participated partially in the dynamometer measurements due to severe muscle weakness. Dixon MRI technique was used to quantify muscle fat fractions and calculate cross-sectional area. Patients with congenital myopathy had lower cross-sectional area in all muscle groups (P<0.01), higher fat fraction (P<0.01) and less strength (P<0.005) in all studied muscle groups. Their fat content was more than doubled and peak torque lower than half that in healthy controls. Muscle contractility was reduced (P<0.01) in three of four patient muscle groups. In conclusion, muscle contractility was reduced in patients with congenital myopathy, across different diagnoses, and was independent of the level of muscle fat fraction, suggesting that intrinsic defects of the myocyte are responsible for reduced contractility.

中文翻译：

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先天性肌病的收缩特性受损

肌肉力量与肌肉截面积的比值称为比力。在许多肌病中都可以看到肌肉的脂肪替代，这会影响比力，但不一定会影响剩余肌纤维的收缩能力。这种能力称为收缩力，是肌肉力量与瘦肌肉横截面积（即收缩横截面积）之间的比率。我们假设先天性肌病患者的收缩力被破坏，因为肌节的收缩蛋白存在缺陷。通过等速测力法测量 16 名先天性肌病患者和 13 名健康对照者的踝关节和膝关节的峰值扭矩。由于严重的肌肉无力，五名患者仅部分参与了测功机测量。Dixon MRI 技术用于量化肌肉脂肪分数并计算横截面积。先天性肌病患者在所有肌肉群中的横截面积较低（P<0.01），脂肪含量较高（P<0.01）和所有研究肌肉群中的力量较小（P<0.005）。他们的脂肪含量是健康对照组的两倍多，峰值扭矩低于健康对照组的一半。四个患者肌肉群中的三个肌群的肌肉收缩力降低 (P<0.01)。总之，不同诊断的先天性肌病患者的肌肉收缩力降低，并且与肌肉脂肪含量水平无关，这表明肌细胞的内在缺陷是导致收缩力降低的原因。先天性肌病患者在所有肌肉群中的横截面积较低（P<0.01），脂肪含量较高（P<0.01）和所有研究肌肉群中的力量较小（P<0.005）。他们的脂肪含量是健康对照组的两倍多，峰值扭矩低于健康对照组的一半。四个患者肌肉群中的三个肌群的肌肉收缩力降低 (P<0.01)。总之，不同诊断的先天性肌病患者的肌肉收缩力降低，并且与肌肉脂肪含量水平无关，这表明肌细胞的内在缺陷是导致收缩力降低的原因。先天性肌病患者在所有肌肉群中的横截面积较低（P<0.01），脂肪含量较高（P<0.01）和所有研究肌肉群中的力量较小（P<0.005）。他们的脂肪含量是健康对照组的两倍多，峰值扭矩低于健康对照组的一半。四个患者肌肉群中的三个肌群的肌肉收缩力降低 (P<0.01)。总之，不同诊断的先天性肌病患者的肌肉收缩力降低，并且与肌肉脂肪含量水平无关，这表明肌细胞的内在缺陷是导致收缩力降低的原因。他们的脂肪含量是健康对照组的两倍多，峰值扭矩低于健康对照组的一半。四个患者肌肉群中的三个肌群的肌肉收缩力降低 (P<0.01)。总之，不同诊断的先天性肌病患者的肌肉收缩力降低，并且与肌肉脂肪含量水平无关，这表明肌细胞的内在缺陷是导致收缩力降低的原因。他们的脂肪含量是健康对照组的两倍多，峰值扭矩低于健康对照组的一半。四个患者肌肉群中的三个肌群的肌肉收缩力降低 (P<0.01)。总之，不同诊断的先天性肌病患者的肌肉收缩力降低，并且与肌肉脂肪含量水平无关，这表明肌细胞的内在缺陷是导致收缩力降低的原因。