Dick Taylor J M, Wakeling James M
Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada
Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada.
J Appl Physiol (1985). 2017 Dec 1;123(6):1433-1442. doi: 10.1152/japplphysiol.01050.2016. Epub 2017 Aug 31.
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. 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.
肌肉收缩时，其厚度或宽度会鼓起，以维持（近乎）恒定的体积。这些动态形状变化与单个肌纤维所受的内部限制紧密相关，并通过增加骨骼肌的工作速度范围，在调节骨骼肌的机械性能方面发挥关键的功能作用。然而，迄今为止，我们对次最大运动条件下体内动态肌肉形状变化的本质及其功能影响了解有限。本研究确定了腓肠肌内侧（MG）肌束速度、羽状角、肌肉厚度以及随后的肌肉传动比在体内如何随力量和速度而变化。为此，我们在一系列踏频和负荷的骑行过程中，使用B型超声记录了MG肌腱长度、肌束长度、羽状角和厚度，并使用表面肌电图记录了肌肉激活情况。我们发现，收缩力增加伴随着肌肉厚度鼓起的减少、羽状角增加的减少以及肌束更快的缩短。尽管由于力-速度效应，肌肉收缩的力量和速度呈负相关，但本研究表明了动态肌肉形状变化如何受力量影响而不受速度影响。在运动过程中，骨骼肌收缩并在厚度或宽度上鼓起。这些形状变化通过增加骨骼肌的工作速度范围，在调节骨骼肌性能方面发挥关键作用。然而，迄今为止，与肌肉形状变化相关的潜在机制在很大程度上仍未得到探索。本研究确定肌肉力量而非速度是在人类骑行过程中使肌肉传动比根据收缩条件而变化的机制驱动因素。
