Department of Motion and Exercise Science, Institute of Sport and Movement Science, University of Stuttgart, Stuttgart, Germany.
Department of Biomechanics, Institute of Sport Science, University of Rostock, Rostock, Germany.
J Appl Physiol (1985). 2022 Jul 1;133(1):223-233. doi: 10.1152/japplphysiol.00735.2021. Epub 2022 Jun 2.
Ecccentric muscle contractions are fundamental to everyday life. They occur markedly in jumping, running, and accidents. Following an initial force rise, stretching of a fully activated muscle can result in a phase of decreasing force ("") followed by force redevelopment. However, how the stretch velocity affects "" and force redevelopment remains largely unknown. We investigated the force produced by fully activated single-skinned fibers of rat extensor digitorum longus muscles during long stretches. Fibers were pulled from length 0.85 to 1.3 optimal fiber length at a rate of 1%, 10%, and 100% of the estimated maximum shortening velocity. "" was absent in slow stretches. Medium and fast stretches yielded a clear "" After the initial force peak, forces decreased by 11.2% and 27.8% relative to the initial peak force before rising again. During the last half of the stretch (from 1.07 to 1.3 optimal fiber length, which is within the range of the expected descending limb of the force-length relationship), the linear force slope tripled from slow to medium stretch and increased further by 60% from medium to fast stretch. These results are compatible with forcible cross-bridge detachment and redevelopment of a cross-bridge distribution, and a viscoelastic titin contribution to fiber force. Accounting for these results can improve muscle models and predictions of multibody simulations. Eccentric muscle contractions are part of our daily lives. We found that force increased monotonically during slow stretches of fully activated muscle fibers, whereas higher stretch velocities resulted in an increasing drop in force after an initial increase and a final steeper rise in force. Cross-bridges cannot explain the observed force traces. This requires a viscoelastic non-cross-bridge contribution. Considering these results can improve muscle models and predictions of multibody simulations.
离心肌肉收缩是日常生活的基础。它们在跳跃、跑步和事故中明显发生。在初始力上升之后，完全激活的肌肉的拉伸可以导致力下降的阶段（“”），然后是力的重新发展。然而，伸展速度如何影响“”和力的重新发展在很大程度上仍然未知。我们研究了完全激活的大鼠伸趾长肌单皮纤维在长时间拉伸过程中产生的力。纤维从长度 0.85 拉伸到 1.3 最佳纤维长度，拉伸速度分别为估计最大缩短速度的 1%、10%和 100%。在缓慢拉伸中，“”不存在。中速和高速拉伸产生了明显的“”。在初始力峰值之后，力相对于初始峰值力下降了 11.2%和 27.8%，然后再次上升。在拉伸的最后一半（从 1.07 到 1.3 最佳纤维长度，这在力-长度关系的预期下降支范围内），从中速到高速拉伸，线性力斜率增加了两倍，从缓慢拉伸增加了 60%。这些结果与强制横桥脱离和横桥分布的重新发展以及粘弹性的 Titin 对纤维力的贡献一致。考虑到这些结果，可以改进肌肉模型和多体模拟的预测。离心肌肉收缩是我们日常生活的一部分。我们发现，在完全激活的肌肉纤维的缓慢拉伸过程中，力单调增加，而较高的拉伸速度导致初始增加后力逐渐下降，最终力急剧上升。横桥不能解释观察到的力轨迹。这需要粘弹性的非横桥贡献。考虑到这些结果，可以改进肌肉模型和多体模拟的预测。
