Fine-wire recordings of flexor hallucis brevis motor units up to maximal voluntary contraction reveal a flexible, nonrigid mechanism for force control
Fine-wire recordings of flexor hallucis brevis motor units up to maximal voluntary contraction reveal a flexible, nonrigid mechanism for force control
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DOI：
10.1152/jn.00023.2020
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发表时间：
2020-05-01
影响因子：
2.5
通讯作者：
Cresswell, A. G.
中科院分区：
文献类型：
--
作者：
Aeles, J.;Kelly, L. A.;Cresswell, A. G.
我们目前对足部内在肌肉的神经生理学特性的了解是有限的，特别是在高力量的情况下。因此，本研究旨在研究足部固有肌肉（即拇短屈肌）在自主收缩达到最大自主收缩的 100% 期间单个运动单位的放电特征。我们使用留置细线电极测量了拇短屈肌运动单位的募集阈值和放电率。十名参与者通过施加跖趾屈曲扭矩来达到最大自愿收缩的目标。我们观察了各种等长收缩力（最大自主收缩的 10% 至 98%）以及各种放电速率（初始放电速率为 4.8 至 23.3 Hz，峰值放电速率为 9.5 至 34.2 Hz）的运动单位募集阈值。我们进一步观察到募集阈值和放电率的高变异性模式以及同一参与者内运动单位之间放电率的交叉。这些发现表明，肌肉的力输出是通过具有显着可变性的机制产生的，而不是依赖于刚性组织，这与所提出的洋葱皮理论相反。在高力和低力任务期间对足底内在足部肌肉的需求可以解释这些观察到的神经生理学特性。新的和值得注意的我们首次记录了拇短屈肌（一种短脚趾肌肉）在最大自主收缩的整个范围内的单运动单位动作电位训练。其运动单位的募集达到非常高（98%）的募集阈值，并且放电率范围很大。我们进一步显示出放电率交叉的高度变异性作为参与者之间和参与者内运动单位之间的招募阈值的函数。
Our current knowledge on the neuro-physiological properties of intrinsic foot muscles is limited, especially at high forces. This study therefore aimed to investigate the discharge characteristics of single motor units in an intrinsic foot muscle, namely flexor hallucis brevis, during voluntary contractions up to 100% of maximal voluntary contraction. We measured the recruitment threshold and discharge rate of flexor hallucis brevis motor units using indwelling fine-wire electrodes. Ten participants followed a target ramp up to maximal voluntary contraction by applying a metatarso-phalangeal flexion torque. We observed motor unit recruitment thresholds across a wide range of isometric forces (ranging from 10 to 98% of maximal voluntary contraction) as well as across a wide range of discharge rates (ranging from 4.8 to 23.3 Hz for initial discharge rate and 9.5 to 34.2 Hz for peak discharge rate). We further observed patterns of high variability in recruitment threshold and discharge rate as well as crossover in discharge rate between motor units within the same participant. These findings suggest that the force output of a muscle is generated through a mechanism with substantial variability rather than relying on a rigid organization, which is in contrast to the proposed onion-skin theory. The demands placed on the plantar intrinsic foot muscles during high- and low-force tasks may explain these observed neurophysiological properties.NEW & NOTEWORTHY We recorded for the first time single motor unit action potential trains in the flexor hallucis brevis, a short toe muscle, over the full range of maximum voluntary contraction. Its motor units are recruited up to very high (98%) recruitment thresholds with a substantial range of discharge rates. We further show high variability with crossover of discharge rates as a function of recruitment threshold both between participants and between motor units within participants.