Faculty of Kinesiology, The University of Calgary, Calgary, AB, CANADA.
Japan Society for the Promotion of Science, Postdoctoral Fellowships for Research Abroad, Tokyo, JAPAN.
Med Sci Sports Exerc. 2018 Jun;50(6):1186-1191. doi: 10.1249/MSS.0000000000001563.
The isometric muscle force attained after active stretch is greater than that attained in a purely isometric contraction. This property is referred to as residual force enhancement (RFE). Because RFE is thought to be caused by a titin-based passive force, it should be preserved in reduced contractile force states. Therefore, we evaluated the magnitude of RFE in normal and reduced contractile force states.
Skinned fibers of rabbit psoas and soleus (N = 60) were used in all experiments. Reduced contractile force states were induced (i) by using a low Ca concentration (N = 30), (ii) by adding 20 mM butanedione monoxime (N = 15), and (iii) by lowering the pH level (N = 15). Force enhancement and reference isometric tests were conducted for each condition. In the force enhancement tests, fibers were actively stretched from an average sarcomere length of 2.4 to 3.0 μm. The isometric force attained 15 s after the end of stretching was used for analysis. In the isometric reference tests, fibers were activated isometrically at an average sarcomere length of 3.0 μm, and the force at steady state was used for analysis. The absolute and relative magnitudes of RFE were calculated.
The absolute RFE was the same for the normal and reduced contractile force states. Because the isometric reference force was smaller in the reduced contractile force states, the relative RFE was greater in the reduced contractile force than the normal states for all conditions.
RFE was preserved in the reduced contractile force states.
主动拉伸后获得的等长肌肉力大于纯粹的等长收缩所获得的力。这种特性被称为残余力增强（RFE）。由于 RFE 被认为是由基于titin 的被动力引起的，因此它应该在收缩力降低的状态下得以保留。因此，我们评估了正常和收缩力降低状态下 RFE 的幅度。
所有实验均使用兔腰大肌和比目鱼肌的去表皮纤维（N = 60）。通过以下三种方式诱导收缩力降低状态：（i）使用低钙浓度（N = 30），（ii）添加 20 mM 丁二酮单肟（N = 15），和（iii）降低 pH 值（N = 15）。对每种情况进行力增强和参考等长测试。在力增强测试中，纤维从平均肌节长度 2.4 到 3.0 μm 处被主动拉伸。拉伸结束后 15 秒获得的等长力用于分析。在等长参考测试中，纤维在平均肌节长度 3.0 μm 处等长激活，用于分析的是稳定状态的力。计算 RFE 的绝对值和相对值。
正常和收缩力降低状态下的绝对 RFE 相同。由于收缩力降低状态下的等长参考力较小，因此在所有条件下，收缩力降低状态下的相对 RFE 都大于正常状态。
RFE 在收缩力降低的状态下得以保留。
