Herbert R D, Héroux M E, Diong J, Bilston L E, Gandevia S C, Lichtwark G A
Neuroscience Research Australia (NeuRA) and University of New South Wales, Sydney, Australia.
J Physiol. 2015 Jan 15;593(2):441-55. doi: 10.1113/jphysiol.2014.279166. Epub 2014 Dec 15.
The mechanisms by which skeletal muscles lengthen and shorten are potentially complex. When the relaxed human gastrocnemius muscle is at its shortest in vivo lengths it falls slack (i.e. it does not exert any passive tension). It has been hypothesised that when the muscle is passively lengthened, slack is progressively taken up, first in some muscle fascicles then in others. Two-dimensional imaging methods suggest that, once the slack is taken up, changes in muscle length are mediated primarily by changes in the lengths of the tendinous components of the muscle. The aims of this study were to test the hypothesis that there is progressive engagement of relaxed muscle fascicles, and to quantify changes in the length and three-dimensional orientation of muscle fascicles and tendinous structures during passive changes in muscle length. Ultrasound imaging was used to determine the location, in an ultrasound image plane, of the proximal and distal ends of muscle fascicles at 14 sites in the human gastrocnemius muscle as the ankle was rotated passively through its full range. A three-dimensional motion analysis system recorded the location and orientation of the ultrasound image plane and the leg. These data were used to generate dynamic three-dimensional reconstructions of the architecture of the muscle fascicles and aponeuroses. There was considerable variability in the measured muscle lengths at which the slack was taken up in individual muscle fascicles. However, that variability was not much greater than the error associated with the measurement procedure. An analysis of these data which took into account the possible correlations between errors showed that, contrary to our earlier hypothesis, muscle fascicles are not progressively engaged during passive lengthening of the human gastrocnemius. Instead, the slack is taken up nearly simultaneously in all muscle fascicles. Once the muscle is lengthened sufficiently to take up the slack, about half of the subsequent increase in muscle length is due to elongation of the tendinous structures and half is due to elongation of muscle fascicles, at least over the range of muscle-tendon lengths that was investigated (up to ∼60 or 70% of the range of in vivo lengths). Changes in the alignment of muscle fascicles and flattening of aponeuroses contribute little to the total change in muscle length.
骨骼肌伸长和缩短的机制可能很复杂。当放松的人体腓肠肌处于其在体内最短长度时，它会松弛（即不产生任何被动张力）。有人提出，当肌肉被被动拉长时，松弛会逐渐被消除，首先在一些肌束中，然后在其他肌束中。二维成像方法表明，一旦松弛被消除，肌肉长度的变化主要由肌肉腱性成分长度的变化介导。本研究的目的是检验放松的肌束逐渐参与的假设，并量化肌肉长度被动变化期间肌束和腱性结构的长度及三维方向的变化。在踝关节被动旋转其全范围时，使用超声成像来确定人体腓肠肌14个部位肌束近端和远端在超声图像平面中的位置。一个三维运动分析系统记录超声图像平面和腿部的位置及方向。这些数据被用于生成肌束和腱膜结构的动态三维重建。在各个肌束中消除松弛时所测量的肌肉长度存在相当大的变异性。然而，这种变异性并不比与测量程序相关的误差大多少。对这些数据进行的考虑误差之间可能相关性的分析表明，与我们早期的假设相反，在人体腓肠肌被动拉长过程中肌束并非逐渐参与。相反，所有肌束中松弛几乎是同时被消除的。一旦肌肉被充分拉长以消除松弛，至少在所研究的肌肉 - 肌腱长度范围内（高达体内长度范围的约60%或70%），随后肌肉长度增加的约一半是由于腱性结构的伸长，一半是由于肌束的伸长。肌束排列的变化和腱膜的变平对肌肉长度的总变化贡献很小。
