KNB 402 Human Performance Laboratory, Faculty of Kinesiology, The University of Calgary, Calgary, 2500 University Drive NW, Calgary, Alberta T2NIN4, Canada.
J Biomech. 2010 Aug 26;43(12):2394-9. doi: 10.1016/j.jbiomech.2010.04.016. Epub 2010 May 8.
Instantaneous contractile characteristics of skeletal muscle, during movement tasks, can be determined and related to steady state mechanical properties such as the force-length relationship with the use of ultrasound imaging. A previous investigation into the contractile characteristics of the vastus lateralis (VL) during cycling has shown that fascicles operate on the "weak" descending limb of the force-length relationship, thus not taking advantage of the "strong" plateau region. The purpose of this study was to investigate if VL fascicle lengths change from sub-maximal to maximal cycling conditions, and if maximal cycling results in VL fascicle lengths which operate across the plateau of the force-length relationship. Fifteen healthy male subjects (age 20.9+/-1.8yr, wt. 67.0+/-6.3kg, ht. 176.7+/-7.2cm) were tested to establish the maximal force-length relationship for the VL through ten maximal isometric contractions at various knee angles. Subjects then cycled on an SRM cycle ergometer at cadences of 50 and 80 revolutions per minute at 100W, 250W, and maximal effort. Fascicle lengths were determined at crank angles of 0, 90, and 180 degrees . Fascicles operated at or near the plateau of the maximal force-length relationship for maximal cycling, while operating on the descending limb during sub-maximal conditions for both cadences. However, when comparing the fascicle operating range for the sub-maximal cycling conditions to the corresponding sub-maximal force-length relationships, the VL now also operated across the plateau region. We concluded from these results that regardless of cycling effort, the VL operated through the ideal plateau region of the corresponding force-length relationship, hence always working optimally. We hypothesize that this phenomenon is due to the coupling of series elastic compliance and length dependent calcium sensitivity in the VL.
在运动任务中，可以通过超声成像确定骨骼肌的瞬时收缩特性，并将其与稳态机械特性（如力-长度关系）相关联。先前对股外侧肌（VL）在骑行过程中的收缩特性的研究表明，肌束在力-长度关系的“弱”下降支上运作，因此无法利用“强”平台区域。本研究旨在探讨在从亚最大到最大骑行条件下，VL 肌束长度是否发生变化，以及最大骑行是否导致 VL 肌束长度跨越力-长度关系的平台。15 名健康男性受试者（年龄 20.9+/-1.8 岁，体重 67.0+/-6.3kg，身高 176.7+/-7.2cm）接受了测试，以通过在各种膝关节角度下进行的 10 次最大等长收缩来确定 VL 的最大力-长度关系。然后，受试者在 SRM 功率自行车上以 50 和 80 转/分钟的转速，100W、250W 和最大努力进行骑行。肌束长度在曲柄角度为 0、90 和 180 度时确定。在最大骑行时，肌束在最大力-长度关系的平台上或附近运作，而在两个转速下的亚最大条件下在下降支上运作。然而，当将亚最大骑行条件下的肌束工作范围与相应的亚最大力-长度关系进行比较时，VL 现在也在平台区域运作。我们从这些结果中得出结论，无论骑行努力如何，VL 都在相应力-长度关系的理想平台区域内运作，因此始终处于最佳工作状态。我们假设这种现象是由于 VL 中串联弹性顺应性和长度依赖性钙敏感性的耦合所致。
