Noonan Alex M, Mashouri Parastoo, Chen Jackey, Power Geoffrey A, Brown Stephen H M
Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, ON, Canada.
Front Physiol. 2020 Aug 12;11:907. doi: 10.3389/fphys.2020.00907. eCollection 2020.
The passive mechanical behavior of skeletal muscle represents both important and generally underappreciated biomechanical properties with little attention paid to their trainability. These experiments were designed to gain insight into the trainability of muscle passive mechanical properties in both single fibers and fiber bundles. Rats were trained in two groups: 4 weeks of either uphill (UH) or downhill (DH) treadmill running; with a third group as sedentary control. After sacrifice, the soleus (SOL), extensor digitorum longus (EDL), and vastus intermedius (VI) were harvested. One hundred seventy-nine bundles and 185 fibers were tested and analyzed using a cumulative stretch-relaxation protocol to determine the passive stress and elastic modulus. Titin isoform expression was analyzed using sodium dodecyl sulfate vertical agarose gel electrophoresis (SDS-VAGE). Single fibers: passive modulus and stress were greater for the EDL at sarcomere lengths (SLs) ≥ 3.7 μm (modulus) and 4.0 μm (stress) with DH training compared to UH training and lesser for the SOL (SLs ≥ 3.3 μm) with DH training compared with control; there was no effect of UH training. Vastus intermedius was not affected by either training protocol. Fiber bundles: passive modulus and stress were greater for the EDL at SLs ≥ 2.5 μm (modulus) and 3.3 μm (stress) in the DH training group as compared with control, while no affects were observed in either the SOL or VI for either training group. No effects on titin isoform size were detected with training. This study demonstrated that a trainability of passive muscle properties at both the single fiber and fiber bundle levels was not accompanied by any detectable changes to titin isoform size.
骨骼肌的被动力学行为代表了重要且普遍未得到充分重视的生物力学特性，人们很少关注其可训练性。这些实验旨在深入了解单纤维和纤维束中肌肉被动力学特性的可训练性。大鼠分为两组进行训练：一组进行为期4周的上坡（UH）跑步机跑步训练，另一组进行为期4周的下坡（DH）跑步机跑步训练；第三组作为久坐对照组。处死后，采集比目鱼肌（SOL）、趾长伸肌（EDL）和股中间肌（VI）。使用累积拉伸-松弛方案对179个纤维束和185根纤维进行测试和分析，以确定被动应力和弹性模量。使用十二烷基硫酸钠垂直琼脂糖凝胶电泳（SDS-VAGE）分析肌联蛋白异构体表达。单纤维：与UH训练相比，在肌节长度（SLs）≥3.7μm（模量）和4.0μm（应力）时，DH训练的EDL的被动模量和应力更大；与对照组相比，在SLs≥3.3μm时，DH训练的SOL的被动模量和应力更小；UH训练没有影响。股中间肌不受任何一种训练方案的影响。纤维束：与对照组相比，在SLs≥2.5μm（模量）和3.3μm（应力）时，DH训练组的EDL的被动模量和应力更大，而在任何一个训练组中，SOL或VI均未观察到影响。训练未检测到对肌联蛋白异构体大小的影响。这项研究表明，在单纤维和纤维束水平上，被动肌肉特性的可训练性并未伴随着肌联蛋白异构体大小的任何可检测到的变化。
