Ettema G J, Huijing P A, van Ingen Schenau G J, de Haan A
Vakgroep Functionele Anatomie, Faculteit Bewegingswetenschappen, Vrije Universiteit Amsterdam, The Netherlands.
J Exp Biol. 1990 Sep;152:333-51. doi: 10.1242/jeb.152.1.333.
Work output of rat gastrocnemius medialis (GM) muscle (N = 5) was measured for stretch-shortening contractions, in which initiation of stretch occurred prior to the onset of activation, and for contractions with an isometric prephase. Duration of the active prephase (prestretch and pre-isometric) varied from 20 to 200 ms. Subsequent shortening (from optimum length + 4 mm to optimum length -2mm) lasted 150 ms. Stretch velocities of 5, 10 and 20 mm s-1 were used, and the shortening velocity was 40 mm s-1. The effects of several combinations of active stretch duration and active stretch amplitude were compared. Using force-compliance characteristics, the work of the contractile element (CE), elastic energy storage and release of the undamped series elastic component (SEC) were distinguished. During shortening, an extra amount of work output was produced, induced by active stretch, of which the largest contribution (70-80%) was due to higher elastic energy release. Enhancement of the storage and utilization of elastic energy during the stretch-shortening cycle, caused by higher transition-point forces (i.e. force at onset of shortening), increased with active stretch amplitude and was associated with a net loss of work, probably due to cross-bridge detachment during active stretch. Net work over the stretch-shortening cycle remained positive for all prestretch contractions, indicating that when a muscle performs this type of contraction, it is able to contribute to work performance on body segments. It is concluded that, in stretch-shortening movements of rat GM muscle, maximal positive work output is incompatible with maximal net work output. Consequences for complex movements in vivo are discussed.
对5只大鼠的腓肠肌内侧（GM）肌肉进行了工作输出测量，测量了拉伸-缩短收缩（其中拉伸在激活开始之前启动）以及具有等长预收缩阶段的收缩。主动预收缩阶段（预拉伸和预等长）的持续时间从20毫秒到200毫秒不等。随后的缩短（从最佳长度+4毫米到最佳长度-2毫米）持续150毫秒。使用了5、10和20毫米/秒的拉伸速度，缩短速度为40毫米/秒。比较了几种主动拉伸持续时间和主动拉伸幅度组合的影响。利用力-顺应特性，区分了收缩元件（CE）的功、弹性能量储存和无阻尼串联弹性成分（SEC）的能量释放。在缩短过程中，主动拉伸诱导产生了额外的功输出，其中最大的贡献（70-80%）来自更高的弹性能量释放。由于更高的过渡点力（即缩短开始时的力），拉伸-缩短循环中弹性能量储存和利用的增强随着主动拉伸幅度的增加而增加，并且与功的净损失相关，这可能是由于主动拉伸过程中的横桥脱离。对于所有预拉伸收缩，拉伸-缩短循环中的净功均保持为正，这表明当肌肉进行这种类型的收缩时，它能够对身体节段的工作表现做出贡献。得出的结论是，在大鼠GM肌肉的拉伸-缩短运动中，最大正功输出与最大净功输出不相容。讨论了对体内复杂运动的影响。
