Groeber Martin, Stafilidis Savvas, Seiberl Wolfgang, Baca Arnold
Department of Biomechanics, Kinesiology and Computer Science in Sport, Centre for Sport Science and University Sports, University of Vienna, Vienna, Austria.
Department of Human Movement Science, Institute of Sport Science, Bundeswehr University Munich, Neubiberg, Germany.
Front Physiol. 2020 Nov 12;11:592183. doi: 10.3389/fphys.2020.592183. eCollection 2020.
In everyday muscle action or exercises, a stretch-shortening cycle (SSC) is performed under different levels of intensity. Thereby, compared to a pure shortening contraction, the shortening phase in a SSC shows increased force, work, and power. One mechanism to explain this performance enhancement in the SSC shortening phase is, besides others, referred to the phenomenon of stretch-induced increase in muscle force (known as residual force enhancement; rFE). It is unclear to what extent the intensity of muscle action influences the contribution of rFE to the SSC performance enhancement. Therefore, we examined the knee torque, knee kinematics, m. vastus lateralis fascicle length, and pennation angle changes of 30 healthy adults during isometric, shortening (CON) and stretch-shortening (SSC) conditions of the quadriceps femoris. We conducted maximal voluntary contractions (MVC) and submaximal electrically stimulated contractions at 20%, 35%, and 50% of MVC. Isometric trials were performed at 20° knee flexion (straight leg: 0°), and dynamic trials followed dynamometer-driven ramp profiles of 80°-20° (CON) and 20°-80°-20° (SSC), at an angular velocity set to 60°/s. Joint mechanical work during shortening was significantly ( < 0.05) enhanced by up to 21% for all SSC conditions compared to pure CON contractions at the same intensity. Regarding the steady-state torque after the dynamic phase, we found significant torque depression for all submaximal SSCs compared to the isometric reference contractions. There was no difference in the steady-state torque after the shortening phases between CON and SSC conditions at all submaximal intensities, indicating no stretch-induced rFE that persisted throughout the shortening. In contrast, during MVC efforts, the steady-state torque after SSC was significantly less depressed compared to the steady-state torque after the CON condition ( = 0.034), without significant differences in the m. vastus lateralis fascicle length and pennation angle. From these results, we concluded that the contribution of the potential enhancing factors in SSCs of the m. quadriceps femoris is dependent on the contraction intensity and the type of activation.
在日常肌肉活动或锻炼中，伸展 - 缩短循环（SSC）在不同强度水平下进行。因此，与单纯的缩短收缩相比，SSC中的缩短阶段表现出更大的力量、功和功率。除其他因素外，解释SSC缩短阶段这种性能增强的一种机制是肌肉力量拉伸诱导增加的现象（称为残余力量增强；rFE）。目前尚不清楚肌肉活动强度在多大程度上影响rFE对SSC性能增强的贡献。因此，我们研究了30名健康成年人在股四头肌等长、缩短（CON）和伸展 - 缩短（SSC）状态下的膝关节扭矩、膝关节运动学、股外侧肌束长度和羽状角变化。我们进行了最大自主收缩（MVC）以及在MVC的20%、35%和50%时的次最大电刺激收缩。等长试验在膝关节屈曲20°（直腿：0°）时进行，动态试验遵循测力计驱动的80° - 20°（CON）和20° - 80° - 20°（SSC）的斜坡轮廓，角速度设定为60°/秒。与相同强度下的纯CON收缩相比，所有SSC状态下缩短过程中的关节机械功显著（<0.05）提高了21%。关于动态阶段后的稳态扭矩，我们发现与等长参考收缩相比，所有次最大SSC均有显著的扭矩下降。在所有次最大强度下，CON和SSC状态下缩短阶段后的稳态扭矩没有差异，表明在整个缩短过程中没有持续的拉伸诱导rFE。相反，在MVC努力期间，与CON状态后的稳态扭矩相比，SSC后的稳态扭矩下降明显较小（=0.034），股外侧肌束长度和羽状角没有显著差异。从这些结果中，我们得出结论，股四头肌SSC中潜在增强因素的贡献取决于收缩强度和激活类型。
