Characteristics and acute responses of eccentric exercise

doi:10.3969/j.issn.2095-4344.0225

Abstract

Abstract:

BACKGROUND: Eccentric exercise displays many advantages over concentric and isometric contractions, and it has been applied in exercise training and rehabilitation. The existing researches focus on the underlying mechanisms at molecular and neural levels, and the specific adaptation after eccentric exercise may be related to the adaptive signaling pathway.
OBJECTIVE: To review the unique physiological characteristics and mechanisms of eccentric exercise, thereby providing reference for in-depth understanding of eccentric exercise.
METHODS: The relevant articles were searched in PubMed (1990-2017) and CNKI (2010-2017) with the keywords of “eccentric exercise, negative muscle work, eccentric exercise training, downhill run, concentric exercise, positive muscle work, concentric exercise training, and uphill running” in English and Chinese, respectively. Ultimately, the articles eligible for physiological characteristics, acute response and adaptive mechanism were enrolled.
RESULTS AND CONCLUSION: Totally 98 articles were retrieved, and 54 pertinent papers were enrolled for analysis based on the inclusion and exclusion criteria. The mechanical, molecular and neural mechanisms of eccentric contractions differ from those of concentric and isometric contractions. Special metabolic and cardiorespiratory responses after eccentric exercise reflect the advantages in making programs of exercise training and rehabilitation. Particularly, compared with concentric exercise, fewer motor units are recruited during eccentric exercise and exert muscle a greater stimulation, which involves the process of exercise-induced muscle damage and the activation of satellite cells. The content of satellite cells after eccentric exercise is higher than that of concentric exercise, suggesting that satellite cells may play an important role in the muscle damage reconstruction caused by eccentric exercise. In conclusion, eccentric exercise is of great significance for exercise training and rehabilitation, while further study on the adaptive mechanism of eccentric exercise is necessary.

中国组织工程研究杂志出版内容重点：组织构建；骨细胞；软骨细胞；细胞培养；成纤维细胞；血管内皮细胞；骨质疏松；组织工程

Key words: Tissue Engineering, Muscle, Skeletal, Mitochondria

CLC Number:

R318

Xu Zhi-yong1, Yin Xin2, Huang Qiang-nian3, Xu Sheng-jia3. Characteristics and acute responses of eccentric exercise[J]. Chinese Journal of Tissue Engineering Research, 2018, 22(16): 2607-2612.

Figures/Tables 2

机械学特征：离心训练肌肉收缩的同时涉及到拉伸肌肉的动作；相反，向心训练肌肉收缩的同时肌肉被缩短。离心训练可以产生比肌肉向心训练或者等张训练更大的肌肉力量[1-2]。肌肉离心训练能够产生更大的力量可能是各种特殊性综合的结果，例如横桥移动过程中分子水平上的变化特殊的神经控制方式[3-4]。因此，在肌肉做离心运动的过程中，可能会给肌肉带来一个更高水平的机械学刺激，并且这个可能潜在的作用于离心训练方案后的骨骼肌机械学上的适应。肌肉离心动作激活策略的特殊性可能主要因为其更大的肌肉输出。大脑皮质激活的更早，并且在肌肉离心动作过程中活动的更加剧烈[5]，在一个相同的机械功率输出情况下，肌肉离心训练过程中股四头肌肌电信号的振幅要比等速向心运动和自行车运动要低[6]。因此，每一条肌纤维产生的张力和肌肉周围组织(如细胞外基质)产生的张力可能在离心运动中都比较高，由此导致了离心活动更多的肌肉输出。分子学特征：肌肉收缩过程中，粗肌丝和细肌丝长度不变，肌纤维长度的变化是通过两者之间重叠程度增加实现的，也就是肌丝滑行学说。这个滑行力来自于两个肌丝重叠部分，肌球蛋白横桥结构，肌球蛋白朝向肌动蛋白上的结合位点重复的相互作用，每一次接触都产生移动的力量[7]。并且每一个横桥上的活动在一个肌节以致整个肌肉都是独立的，不受其他横桥上活动的影响，这样才可能使肌肉产生恒定的张力和连续的缩短，而且横桥激活的数目直接影响了肌张力和缩短的距离。这个过程有效的解释了向心和等长肌肉收缩动作。等长肌肉收缩时，肌肉长度不变，横桥与肌动蛋白的相互作用仍然存在，这时横桥与肌动蛋白自然分离，并被其他新的桥取代来维持横桥网络的形成，这样尽管缺少外部的身体活动，仍然能产生能量。上面是已建立经典的肌肉收缩理论，基于此理论有人进一步提出假设，在离心收缩时，横桥并未完成一次完整的横桥周期[8]，它们在肌动蛋白边界变得高度活跃，在迅速接触肌动蛋白结合位点后立即被强行分离，这是因为完整的横桥周期没有完成，较少的ATP是维持力量的一个必要条件[9]。神经学特征：与向心收缩相比，离心收缩过程中更少的运动单元被募集，并且放电率也更低[10-12]。皮质兴奋性在离心收缩过程中被加强，并且不被离心收缩的负重情况和较低的运动单位募集度影响[5，13]。这个过程的具体机制现在仍然不是很清楚，可能和运动皮质的输出量降低或来自外周神经的促进突触前抑制的增加有关[10]。总之，现有的肌丝滑行理论很难解释离心收缩过程中产生的更大的肌力以及低能量消耗，结合横桥分离理论，可能有助于理解认识离心运动的诸多特性。相比于向心收缩和等长收缩，不论在最大收缩或次最大收缩情况下，离心收缩显示出独特的神经策略。这些差异可能主要与脊髓抑制的调停有关，需要更加精确的数据来证明。大强度的力量训练被有效用于降低最大离心收缩过程中的反射抑制，从而诱导改善神经肌肉活性和提高肌肉最大离心力量[14]。 2.2.2 离心运动的急性反应代谢和心肺反应：肌肉离心动作机械学和代谢学的特异性已经在人和动物身上被研究。当进行相同的机械功输出的前提下，急性离心运动后的代谢和心肺反应与向心运动反应情况不同，运动过程中尤其要控制离心运动的训练负荷和强度。在一个既定的机械功输出前提下，离心运动比向心运动代谢需求更低[15]，并且相同的工作效率时，离心运动需要更少的运动单位参与[16]。其次，摄氧量在存在不同，进行速度为4.8 km/h的下坡走(坡度-5°至-15°)，氧气消耗(VO2)要比相同速度下进行水平走或者上坡走的VO2要低[17]。并且在增加运动强度提高代谢需求的下坡跑实验中，在相同的、速度的前提下，下坡跑比上坡跑的VO2也要低四五倍[18]。这说明相比于向心运动，离心运动的能量消耗低，这也让离心运动更加适合运用于衰老人群的肌肉质量和力量恢复以及临床康复中[11，19]。尽管离心运动被认为是“节省能量”的，但是离心运动可能会增加运动后的安静状态下能量消耗，并在运动后 72 h仍然能够观察到此现象[20]。Gavin等[21]近期研究表明较低的肌糖原对运动型肌损伤后的代谢和心肺反应有影响，在下坡跑后12 h，较低的肌糖原组脂肪氧化率增加，并且减少了碳水化合物，表明损伤性的运动伴随糖原减少在之后的低强度离心运动后仅12 h便能够增加脂肪利用率。这表明离心运动独特的代谢反应和适应，运动后安静状态能量消耗增加可能和离心运动对肌肉刺激大导致运动后生物适应带来的表型变化有关，需要进一步证据证实以及机制的研究。如果肌肉离心模式中机械功输出足够大的话(例如：功率自行车运动中肌肉离心活动是肌肉向心活动机械功输出的5倍，能够完成一次离心运动与向心运动相似的VO2。在这种特定的情况下，离心运动的心输出量(Q)和心率(HR)都比向心运动要高。在绝对摄氧量接近或高于1 L/min时，这个特性更加明显，肌肉离心活动的心输出量和心率分别比肌肉向心活动高了17%-27%[17]。这个现象对于运动训练强度和负荷的控制具有重要的影响，此外，一个既定的心率在离心和向心运动中对应不同水平的VO2。在相同心率情况下离心运动中的VO2会比向心运动中的VO2要低，这表明在相同的VO2下运动，离心运动需要比向心运动更高的心率[17]。根据现有研究，离心运动的这些生理反应在自行车运动中更加明显，提示离心自行车运动可能是一个研究离心运动的理想模型，能够在保证大强度机械刺激的同时带来较低的代谢刺激。因此，需要根据肌肉工作不同类型和模式研究心率，以监控运动强度和训练负荷。分子水平反应：已有研究表明运动能够激活卫星细胞，在运动性肌损伤后的肌肉修复过程以及随后的肥大适应过程中卫星细胞发挥了至关重要的作用[22]。卫星细胞是骨骼肌中位于肌细胞膜和基膜之间具有增殖分化潜力的肌源性细胞。Hyldahl等[23]研究发现当肌细胞受损后，卫星细胞能够增殖并到达受损肌细胞，参与到肌细胞重建和修复过程中，而且卫星细胞的激活可能与运动方式有关，最大离心力量训练能够诱发卫星细胞在运动后剧烈增殖，而在向心力量训练后却没有发生，这提示运动造成肌损伤过程中离心运动的部分可能是激活卫星细胞的主要因素。目前研究已经很好的证实了离心训练能够增加肌细胞核数量和卫星细胞含量[24]。在最大等速离心运动后24 h，卫星细胞含量从30%增加到150%，卫星细胞含量的大幅增加说明肌肉在受到最大离心运动刺激后需要更多卫星细胞的激活，从而满足肌肉重建和修复的急性需求。卫星细胞的增加还和肌纤维类型有关，在最大离心运动后发现卫星细胞活性在Ⅱ型肌纤维中显著增加，而在Ⅰ型肌纤维中却没有显著变化[24]。另外有研究表明，卫星细胞激活的信号分子白细胞介素6(IL-6)在离心运动后急性期升高，而白细胞介素6在肌损伤急性免疫反应中发挥作用[25]。肌肉肥大是运动训练中关键的适应性反应，涉及到肌纤维蛋白合成的过程，而相比于最大向心运动，最大等速离心运动能够更多的诱发肌纤维蛋白迅速生成，并在接下来的恢复期形成肌肉肥大[26]。最近研究表明肌肉在生长和修复期间，卫星细胞和骨骼肌中的细胞外基质之间的相互作用在肌肉适应过程中发挥重要的作用，卫星细胞在激活时可通过自我更新或增殖产生肌原性祖细胞(MPCs)，后者能够迁移到细胞外基质中，并能通过分泌含有microRNA-206的外泌体(exosome)，抑制核糖体结合蛋白1抗体(Rrbp1)从而调节纤维形成细胞胶原表达，肌原性祖细胞在运动后肌肉肥大适应过程中发挥着防止细胞外基质的过度沉积、促进长期肌纤维肥大的重要作用，而microRNA-206在其中发挥重要的负调控作用[22]。目前已知的几种肌肉特异性的microRNAs(myomiRs)可能在离心运动生物适应过程中发挥重要的调控作用，见表1。"

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