Shifting gears: dynamic muscle shape changes and force-velocity behavior in the medial gastrocnemius
Shifting gears: dynamic muscle shape changes and force-velocity behavior in the medial gastrocnemius
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DOI：
10.1152/japplphysiol.01050.2016
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发表时间：
2017-12-01
影响因子：
3.3
通讯作者：
Wakeling, James M.
中科院分区：
文献类型：
--
作者：
Dick, Taylor J. M.;Wakeling, James M.
当肌肉收缩时，它们的厚度或宽度会膨胀，以保持（几乎）恒定的体积。这些动态形状变化与施加在个体肌纤维上的内部约束紧密相关，并且通过增加其操作速度范围在调节骨骼肌的机械性能中发挥关键的功能作用。然而，到目前为止，我们有一个有限的了解，在体内动态肌肉形状变化的性质和功能的影响下，次最大的条件。本研究确定了如何在体内的变化，内侧腓肠肌（MG）束速度，pennation角，肌肉厚度，随后的肌肉齿轮变化的力和速度的函数。要做到这一点，我们获得了MG肌腱长度，肌束长度，pennation角，厚度使用B型超声和肌肉激活使用表面肌电图在一系列的节奏和负荷骑自行车。我们发现，收缩力的增加伴随着肌肉厚度的减少，羽状角的增加减少，以及更快的肌束缩短。虽然肌肉收缩的力和速度是负相关的，由于力-速度效应，这项研究表明动态肌肉形状的变化是如何受到力的影响，而不是速度的影响。新&值得注意的是在运动过程中，骨骼肌收缩和厚度或宽度的凸起。这些形状变化通过增加骨骼肌的工作速度范围在调节骨骼肌的性能方面起着关键作用。然而，迄今为止，与肌肉形状变化相关的潜在机制仍在很大程度上未被探索。这项研究确定了肌肉力量，而不是速度，作为机械驱动因素，允许肌肉齿轮变化取决于人类骑自行车期间的收缩条件。
When muscles contract, they bulge in thickness or in width to maintain a (nearly) constant volume. These dynamic shape changes are tightly linked to the internal constraints placed on individual muscle fibers and play a key functional role in modulating the mechanical performance of skeletal muscle by increasing its range of operating velocities. Yet to date we have a limited understanding of the nature and functional implications of in vivo dynamic muscle shape change under submaximal conditions. This study determined how the in vivo changes in medial gastrocnemius (MG) fascicle velocity, pennation angle, muscle thickness, and subsequent muscle gearing varied as a function of force and velocity. To do this, we obtained recordings of MG tendon length, fascicle length, pennation angle, and thickness using B-mode ultrasound and muscle activation using surface electromyography during cycling at a range of cadences and loads. We found that that increases in contractile force were accompanied by reduced bulging in muscle thickness, reduced increases in pennation angle, and faster fascicle shortening. Although the force and velocity of a muscle contraction are inversely related due to the force-velocity effect, this study has shown how dynamic muscle shape changes are influenced by force and not influenced by velocity.NEW & NOTEWORTHY During movement, skeletal muscles contract and bulge in thickness or width. These shape changes play a key role in modulating the performance of skeletal muscle by increasing its range of operating velocities. Yet to date the underlying mechanisms associated with muscle shape change remain largely unexplored. This study identified muscle force, and not velocity, as the mechanistic driving factor to allow for muscle gearing to vary depending on the contractile conditions during human cycling.