DOI of the published article https://doi.org/10.1152/jn.00462.2022
Intrinsic motor neurone excitability is increased after resistance training in older adults
DOI:
https://doi.org/10.51224/SRXIV.144Keywords:
Persistent Inward Currents, Motor Unit, Strength Training, AgingAbstract
This study investigated the effects of high-intensity resistance training on estimates of the motor neurone persistent inward current (PIC) in older adults. Seventeen participants (68.5±2.8 years) completed a 2-week non-exercise control period followed by 6 weeks of resistance training. Surface electromyographic signals were collected using 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 (a) triangular-shaped contractions to 20% of maximum torque capacity, and (b) 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 pps; p≤0.015) and peak discharge rates (0.78-0.99 pps; p≤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- and 40% triangular-shaped contractions were 0.09-0.18 pps (p=0.448 and 0.109, respectively), which increased to 0.44 pps (p<0.001) after training. Also, moderate-to-very large correlations (r=0.39-0.82) were observed between changes in 20% triangular-shaped contraction ΔF and changes in peak discharge rates and broad measures of motor function. Our findings indicate, for the first time, that increased motor neurone excitability is a potential mechanism underpinning training-induced improvements in motor neurone 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.
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Copyright (c) 2022 Lucas B R Orssatto, Patrick Rodrigues, Karen Mackay Phillips, Anthony J. Blazevich, David N. Borg, Tiago R Souza, Raphael L. Sakugawa, Anthony J. Shield, Gabriel S. Trajano
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