Neptune R R, Herzog W
Human Performance Laboratory, Faculty of Kinesiology, Univesity of Calgary, Canada.
J Biomech. 2000 Feb;33(2):165-72. doi: 10.1016/s0021-9290(99)00149-9.
The objective of this work was to increase our understanding of how motor patterns are produced during movement tasks by quantifying adaptations in muscle coordination in response to altered task mechanics. We used pedaling as our movement paradigm because it is a constrained cyclical movement that allows for a controlled investigation of test conditions such as movement speed and effort. Altered task mechanics were introduced using an elliptical chainring. The kinematics of the crank were changed from a relatively constant angular velocity using a circular chainring to a widely varying angular velocity using an elliptical chainring. Kinetic, kinematic and muscle activity data were collected from eight competitive cyclists using three different chainrings--one circular and two different orientations of an elliptical chainring. We tested the hypotheses that muscle coordination patterns (EMG timing and magnitude), specifically the regions of active muscle force production, would shift towards regions in the crank cycle in which the crank angular velocity, and hence muscle contraction speeds, were favorable to produce muscle power as defined by the skeletal muscle power-velocity relationship. The results showed that our hypothesis with regards to timing was not supported. Although there were statistically significant shifts in muscle timing, the shifts were minor in absolute terms and appeared to be the result of the muscles accounting for the activation dynamics associated with muscle force development (i.e. the delay in muscle force rise and decay). But, significant changes in the magnitude of muscle EMG during regions of slow crank angular velocity for the tibialis anterior and rectus femoris were observed. Thus, the nervous system used adaptations to the muscle EMG magnitude, rather than the timing, to adapt to the altered task mechanics. The results also suggested that cyclists might work on the descending limb of the power-velocity relationship when pedaling at 90 rpm and sub-maximal power output. This finding might have important implications for preferred pedaling rate selection.
这项工作的目的是通过量化肌肉协调对改变的任务力学的适应性，来增进我们对运动任务中运动模式如何产生的理解。我们选择蹬踏作为运动范式，因为它是一种受限的周期性运动，便于对诸如运动速度和用力等测试条件进行可控研究。使用椭圆链轮来引入改变的任务力学。曲柄的运动学从使用圆形链轮时相对恒定的角速度，变为使用椭圆链轮时变化很大的角速度。使用三个不同的链轮（一个圆形和两个不同方向的椭圆链轮）从八名竞技自行车运动员身上收集了动力学、运动学和肌肉活动数据。我们检验了以下假设：肌肉协调模式（肌电图的时间和幅度），特别是主动肌肉力量产生的区域，会朝着曲柄周期中曲柄角速度以及因此肌肉收缩速度有利于产生由骨骼肌功率-速度关系定义的肌肉功率的区域转移。结果表明，我们关于时间的假设未得到支持。尽管肌肉时间上有统计学上的显著变化，但绝对变化很小，似乎是肌肉考虑了与肌肉力量发展相关的激活动力学（即肌肉力量上升和下降的延迟）的结果。但是，观察到在胫骨前肌和股直肌的曲柄角速度较慢区域，肌肉肌电图幅度有显著变化。因此，神经系统利用对肌肉肌电图幅度而非时间的适应性来适应改变的任务力学。结果还表明，自行车运动员在以90转/分钟的转速和次最大功率输出蹬踏时，可能处于功率-速度关系的下降阶段。这一发现可能对首选蹬踏速率的选择有重要意义。
