Abstract：
Persistent inward currents (PICs) increase the intrinsic excitability of α-motoneurons. The main objective of this study was to compare estimates of α-motoneuronal PICs between inactive, chronic resistance-trained, and chronic endurance-trained young individuals. We also aimed to investigate whether there is a relationship in the estimates of α-motoneuronal PIC magnitude between muscles. Estimates of PIC magnitude were obtained in three groups of young individuals: resistance-trained (n = 12), endurance-trained (n = 12), and inactive (n = 13). We recorded high-density surface electromyography (HDsEMG) signals from tibialis anterior (TA), gastrocnemius medialis (GM), soleus (SOL), vastus medialis (VM), and vastus lateralis (VL). Then, signals were decomposed with convolutive blind source separation to identify motor unit (MU) spike trains. Participants performed triangular isometric contractions to a peak of 20% of their maximum voluntary contraction. A paired-motor-unit analysis was used to calculate ΔF, which is assumed to be proportional to PIC magnitude. Despite the substantial differences in physical training experience between groups, we found no differences in ΔF, regardless of the muscle. Significant correlations of estimates of PIC magnitude were found between muscles of the same group (VL-VM, SOL-GM). Only two correlations (out of 8) between muscles of different groups were found (TA-GM and VL-GM). Overall, our findings suggest that estimates of PIC magnitude from lower-threshold MUs at low contraction intensities in the lower limb muscles are not influenced by physical training experience in healthy young individuals. They also suggest muscle-specific and muscle group-specific regulations of the estimates of PIC magnitude.NEW & NOTEWORTHY Chronic resistance and endurance training can lead to specific adaptations in motor unit activity. The contribution of α-motoneuronal persistent inward currents (PICs) to these adaptations is currently unknown in healthy young individuals. Therefore, we studied whether estimates of α-motoneuronal PIC magnitude are higher in chronically trained endurance- and resistance-trained individuals. We also studied whether there is a relationship between the estimates of α-motoneuronal PIC magnitude of different lower limb muscles.
摘要：
持续的内向电流（PIC）增加了α运动神经元的内在兴奋性。这项研究的主要目的是比较不活跃，慢性抵抗力训练和慢性耐力训练的年轻人。我们还旨在研究肌肉之间α-运动神经元PIC大小的估计值是否存在关系。在三组年轻人中获得了PIC大小的估计：抵抗训练（n=12），耐力训练(n=12)，和不活跃（n=13）。我们记录了胫骨前肌的高密度表面肌电图（HDsEMG）信号，中腓肠肌,比目鱼,中肌,和股外侧肌。然后，用卷积盲源分离对信号进行分解，以识别电机单元尖峰序列。参与者进行了三角等距收缩，达到其最大自愿收缩的20％的峰值。使用成对运动单元分析来计算ΔF，假定与PIC大小成正比。尽管在体能训练经验上两组之间有很大的差异,我们发现ΔF没有差异，不管肌肉。在同一组的肌肉之间发现了PICs大小估计值的显着相关性（VL-VM，SOL-GM)。在不同组的肌肉之间仅发现一种相关性(8种)(GM和TA)。总的来说,我们的研究结果表明,在健康的年轻人中,在下肢肌肉低收缩强度下,低阈值MU对PIC大小的估计不受体育锻炼经验的影响.他们还建议对PIC大小的估计进行肌肉特异性和肌肉群特异性调节。
