It has been suggested that cross bridge kinetics and residual force enhancement (RFE) affect force in the stretch-shortening cycle (SSC). Because cross bridge kinetics and titin isoforms, which are thought to be related to RFE, differ between muscles, the SSC effect may be also muscle-dependent. Thus, we compared the SSC effect between psoas and soleus muscles, which have a distinct fiber type distribution and different titin isoforms. Four tests (SSC, SSC control, RFE, RFE control) were conducted using isolated, skinned fibers of psoas and soleus. In the SSC tests, fibers were activated at an average sarcomere length of 2.4 μm, stretched to 3.0 μm, and shortened to 2.4 μm. In the SSC control tests, fibers were activated at an average sarcomere length of 3.0 μm and then shortened to 2.4 μm. The relative increase in mechanical work obtained during shortening between tests was defined as the SSC effect. In the RFE tests, fibers were activated at an average sarcomere length of 2.4 μm and then stretched to 3.0 μm, while the RFE control tests consisted of an isometric contraction at 3.0 μm. The difference in steady-state isometric force between tests was defined as RFE. The SSC effect was greater in soleus than in psoas, while the RFE was the same for both muscles. Since the SSC effect was greater in soleus, while the RFE was the same, the observed greater SSC effect is probably not directly caused by RFE, but may be related to differences in cross bridge kinetics.

已经提出，跨桥动力学和残余力增强（RFE）影响拉伸缩短循环（SSC）中的力。因为跨桥动力学和认为与RFE相关的替丁同工型在肌肉之间存在差异，所以SSC效应也可能与肌肉有关。因此，我们比较了腰肌和比目鱼肌之间的SSC效应，它们具有明显的纤维类型分布和不同的肌动蛋白亚型。使用腰大肌和比目鱼的隔离，有皮肤的纤维进行了四个测试（SSC，SSC对照，RFE，RFE对照）。在SSC测试中，纤维的平均肌节长度为2.4μm，被拉伸至3.0μm，然后缩短至2.4μm。在SSC对照测试中，纤维的平均肌节长度为3.0μm，然后被缩短至2.4μm。在测试之间的缩短期间获得的机械功的相对增加被定义为SSC效应。在RFE测试中，纤维的平均肌节长度为2.4μm，然后被拉伸至3.0μm，而RFE对照测试包括在3.0μm处的等距收缩。试验之间稳态等距力的差异定义为RFE。比目鱼肌的SSC效果比腰肌的效果大，而两条肌肉的RFE相同。由于SSC效应在比目鱼肌中更大，而RFE相同，因此观察到的更大的SSC效应可能不是直接由RFE引起，而是可能与跨桥动力学的差异有关。而RFE对照测试包括3.0μm的等距收缩。试验之间稳态等距力的差异定义为RFE。比目鱼肌的SSC效果比腰肌的效果大，而两条肌肉的RFE相同。由于SSC效应在比目鱼肌中更大，而RFE相同，因此观察到的更大的SSC效应可能不是直接由RFE引起的，而是可能与跨桥动力学的差异有关。而RFE对照测试包括3.0μm的等距收缩。试验之间稳态等距力的差异定义为RFE。比目鱼肌的SSC效果比腰肌的效果大，而两条肌肉的RFE相同。由于SSC效应在比目鱼肌中更大，而RFE相同，因此观察到的更大的SSC效应可能不是直接由RFE引起的，而是可能与跨桥动力学的差异有关。