Bullimore Sharon R, Leonard Tim R, Rassier Dilson E, Herzog Walter
Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, 2500 University Drive NW, Calgary, AB, Canada T2N 1N4.
J Biomech. 2007;40(7):1518-24. doi: 10.1016/j.jbiomech.2006.06.014. Epub 2006 Aug 21.
It is well-recognised that steady-state isometric muscle force is decreased following active shortening (force depression, FD) and increased following active stretch (force enhancement, FE). It has also been demonstrated that passive muscle force is increased following active stretch (passive FE). Several studies have reported that FD increases with shortening amplitude and that FE and passive FE increase with stretch amplitude. Here, we investigate whether these trends continue with further increases in shortening or stretch amplitude. Experiments were performed using in situ cat soleus muscles (n=8 for FD; n=7 for FE and passive FE). FD, FE and passive FE were measured after shortening or stretch contractions that covered as wide a range of amplitudes as practically possible without damaging the muscles. FD increased approximately linearly with shortening amplitude, over the full range of amplitudes investigated. This is consistent with the hypothesis that FD arises from a stress-induced inhibition of crossbridges. FE increased with stretch amplitude only up to a point, and then levelled off. Passive FE, and the transient increase in force at the end of stretch, showed relationships to stretch amplitude that were qualitatively very similar to the relationship for FE, increasing only until the same critical stretch amplitude had been reached. We conclude that FE and passive FE do not increase with stretch amplitude under all circumstances. This finding has important consequences for determining the mechanisms underlying FE and passive FE because any mechanism that is proposed to explain them must be able to predict it.
众所周知，主动缩短后稳态等长肌力会降低（力抑制，FD），而主动拉伸后则会增加（力增强，FE）。也有研究表明，主动拉伸后被动肌力会增加（被动FE）。多项研究报告称，FD随缩短幅度增加，而FE和被动FE随拉伸幅度增加。在此，我们研究随着缩短或拉伸幅度进一步增加，这些趋势是否会持续。实验使用原位猫比目鱼肌进行（FD实验n = 8；FE和被动FE实验n = 7）。在进行尽可能大的幅度范围（不损伤肌肉）的缩短或拉伸收缩后，测量FD、FE和被动FE。在所研究的整个幅度范围内，FD随缩短幅度大致呈线性增加。这与FD源于应力诱导的横桥抑制这一假设一致。FE仅在达到某一点之前随拉伸幅度增加，然后趋于平稳。被动FE以及拉伸结束时力的瞬时增加，与拉伸幅度的关系在定性上与FE的关系非常相似，仅在达到相同的临界拉伸幅度之前增加。我们得出结论，FE和被动FE并非在所有情况下都随拉伸幅度增加。这一发现对于确定FE和被动FE背后的机制具有重要意义，因为任何被提出用于解释它们的机制都必须能够预测这一点。
