Tsatsaki Eirini, Amiridis Ioannis G, Holobar Ales, Trypidakis Georgios, Arabatzi Fotini, Kellis Eleftherios, Enoka Roger M
Department of Physical Education and Sport Sciences at Serres, Aristotle University of Thessaloniki, Serres, Greece.
Faculty of Electrical Engineering and Computer Science, University of Maribor, Maribor, Slovenia.
Eur J Sport Sci. 2022 Apr;22(4):539-548. doi: 10.1080/17461391.2021.1922506. Epub 2021 May 21.
The purpose of the study was to assess the influence of short, intermediate, and long muscle lengths on dorsiflexor force steadiness and the discharge characteristics of motor units in tibialis anterior during submaximal isometric contractions. Steady contractions were performed at 5 target forces (5, 10, 20, 40, and 60% maximal voluntary contraction, MVC) for 3 ankle angles (75°, 90°, and 105°). MVC force was less ( = 0.043) at the smallest joint angle compared with the other two angles. The absolute (standard deviation) and normalised amplitudes (coefficient of variation) of the force fluctuations were similar for all 3 ankle angles at each target force. The coefficient of variation for force decreased progressively from 5% to 20% MVC force and then it plateaued at 40% and 60% MVC force. At all target forces, the mean discharge rate (MDR) of the motor units at 75° was greater than at 90° ( = 0.006) and 105° ( = 0.034). Moreover, the MDR was similar for 5% and 10% MVC forces and then increased gradually until 60% MVC force ( < 0.005). The variability in discharge times (coefficient of variation for interspike interval) and variability in neural drive (coefficient of variation of filtered cumulative spike train) were similar at all ankle angles. Variability in neural drive had a greater influence on force steadiness than did the variability in discharge times. Changes in ankle-joint angle did not influence either the normalised amplitude force fluctuations during steady submaximal contractions or the underlying modulation of the discharge characteristics of motor units in tibialis anterior.
本研究的目的是评估在次最大等长收缩过程中，短、中、长肌肉长度对背屈肌力量稳定性以及胫骨前肌运动单位放电特性的影响。在3个踝关节角度（75°、90°和105°）下，针对5个目标力（5%、10%、20%、40%和60%最大自主收缩，MVC）进行稳定收缩。与其他两个角度相比，最小关节角度时的MVC力较小（ = 0.043）。在每个目标力下，所有3个踝关节角度的力波动的绝对（标准差）和归一化幅度（变异系数）相似。力的变异系数从5% MVC力逐渐下降到20% MVC力，然后在40%和60% MVC力时趋于平稳。在所有目标力下，75°时运动单位的平均放电率（MDR）大于90°（ = 0.006）和105°（ = 0.034）时。此外，5%和10% MVC力时的MDR相似，然后逐渐增加直至60% MVC力（ < 0.005）。在所有踝关节角度下，放电时间的变异性（峰间间隔的变异系数）和神经驱动的变异性（滤波后的累积脉冲序列的变异系数）相似。神经驱动的变异性对力量稳定性的影响大于放电时间的变异性。踝关节角度的变化既不影响次最大稳定收缩过程中的归一化幅度力波动，也不影响胫骨前肌运动单位放电特性的潜在调节。
