Orssatto Lucas B R, Rodrigues Patrick, Mackay Karen, Blazevich Anthony J, Borg David N, Souza Tiago Rosa de, Sakugawa Raphael L, Shield Anthony J, Trajano Gabriel S
School of Exercise and Nutrition Sciences, Faculty of Health, Queensland University of Technology, Brisbane, Queensland, Australia.
Centre for Human Performance, School of Medical and Health Sciences, Edith Cowan University, Joondalup, Western Australia, Australia.
J Neurophysiol. 2023 Mar 1;129(3):635-650. doi: 10.1152/jn.00462.2022. Epub 2023 Feb 8.
This study investigated the effects of high-intensity resistance training on estimates of the motor neuron persistent inward current (PIC) in older adults. Seventeen participants (68.5 ± 2.8 yr) completed a 2-wk nonexercise control period followed by 6 wk of resistance training. Surface electromyographic signals were collected with two 32-channel electrodes placed over soleus to investigate motor unit discharge rates. Paired motor unit analysis was used to calculate delta frequency (ΔF) as an estimate of PIC amplitudes during ) triangular-shaped contractions to 20% of maximum torque capacity and ) trapezoidal- and triangular-shaped contractions to 20% and 40% of maximum torque capacity, respectively, to understand their ability to modulate PICs as contraction intensity increases. Maximal strength and functional capacity tests were also assessed. For the 20% triangular-shaped contractions, ΔF [0.58-0.87 peaks per second (pps); ≤ 0.015] and peak discharge rates (0.78-0.99 pps; ≤ 0.005) increased after training, indicating increased PIC amplitude. PIC modulation also improved after training. During the control period, mean ΔF differences between 20% trapezoidal-shaped and 40% triangular-shaped contractions were 0.09-0.18 pps ( = 0.448 and 0.109, respectively), which increased to 0.44 pps ( < 0.001) after training. Also, changes in ΔF showed moderate to very large correlations ( = 0.39-0.82) with changes in peak discharge rates and broad measures of motor function. Our findings indicate that increased motor neuron excitability is a potential mechanism underpinning training-induced improvements in motor neuron discharge rate, strength, and motor function in older adults. This increased excitability is likely mediated by enhanced PIC amplitudes, which are larger at higher contraction intensities. Resistance training elicited important alterations in soleus intrinsic motor neuronal excitability, likely mediated by enhanced persistent inward current (PIC) amplitude, in older adults. Estimates of PICs increased after the training period, accompanied by an enhanced ability to increase PIC amplitudes at higher contraction intensities. Our data also suggest that changes in PIC contribution to self-sustained discharging may contribute to increases in motor neuron discharge rates, maximal strength, and functional capacity in older adults after resistance training.
本研究调查了高强度抗阻训练对老年人运动神经元持续性内向电流（PIC）估计值的影响。17名参与者（68.5±2.8岁）完成了为期2周的非运动对照期，随后进行了6周的抗阻训练。使用两个32通道电极置于比目鱼肌上采集表面肌电信号，以研究运动单位放电率。配对运动单位分析用于计算三角频率（ΔF），作为PIC幅度的估计值，分别在向最大扭矩能力的20%进行三角形成形收缩以及向最大扭矩能力的20%和40%进行梯形和三角形成形收缩时，以了解随着收缩强度增加它们调节PIC的能力。还评估了最大力量和功能能力测试。对于20%的三角形成形收缩，训练后ΔF[每秒0.58 - 0.87个峰值（pps）；P≤0.015]和峰值放电率（0.78 - 0.99 pps；P≤0.005）增加，表明PIC幅度增加。训练后PIC调节也有所改善。在对照期，20%梯形收缩和40%三角收缩之间的平均ΔF差异为0.09 - 0.18 pps（分别为P = 0.448和0.109），训练后增加到0.44 pps（P<0.001）。此外，ΔF的变化与峰值放电率的变化以及运动功能的广泛指标显示出中度到非常大的相关性（r = 0.39 - 0.82）。我们的研究结果表明，运动神经元兴奋性增加是老年人训练诱导的运动神经元放电率、力量和运动功能改善的潜在机制。这种增加的兴奋性可能由增强的PIC幅度介导，在较高收缩强度下PIC幅度更大。抗阻训练引起了老年人比目鱼肌内在运动神经元兴奋性的重要改变，可能由增强的持续性内向电流（PIC）幅度介导。训练期后PIC的估计值增加，同时在较高收缩强度下增加PIC幅度的能力增强。我们的数据还表明，PIC对自维持放电的贡献变化可能有助于老年人抗阻训练后运动神经元放电率、最大力量和功能能力的增加。
