Abstract
Purpose
The purpose was to examine the effects of 8-weeks (3 days/week) of linear periodization resistance exercise training (RET) on neuromuscular function in prepubescent youth.
Methods
Twenty-five healthy prepubescent youth (11 males, 14 females, age = 9.1 ± 0.8 years) completed the RET (n = 17) or served as controls (CON, n = 8). Isometric maximal voluntary contractions (MVCs) and trapezoidal submaximal contractions at 35 and 60% MVC of the right leg extensors were performed with surface electromyography (EMG) recorded from the leg extensors [vastus lateralis (VL), rectus femoris, and vastus medialis] and flexors (biceps femoris and semitendinosus). EMG amplitude of the leg extensors and flexors were calculated during the MVCs. Motor unit (MU) action potential trains were decomposed from the surface EMG of the VL for the 35 and 60% MVCs. MU firing rates and action potential amplitudes were regressed against recruitment threshold with the y-intercepts and slopes calculated for each contraction. Total leg extensor muscle cross-sectional area (CSA) was collected using ultrasound images. ANOVA models were used to examine potential differences.
Results
Isometric strength increased post-RET (P = 0.006) with no changes in leg extensor and flexor EMG amplitude. Furthermore, there were no changes in total CSA or the MU action potential amplitude vs. recruitment threshold relationships. However, there were increases in the firing rates of the higher-threshold MUs post-RET as indicated with greater y-intercepts (P = 0.003) from the 60% MVC and less negative slope (P = 0.004) of the firing rates vs. recruitment threshold relationships at 35% MVC.
Conclusions
MU adaptations contribute to strength increases following RET in prepubescent youth.
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Data availability
Data is available upon a resonable request.
Abbreviations
- ANOVA:
-
Analysis of variance
- ASIS:
-
Anterior superior iliac spine
- BF:
-
Biceps femoris
- CON:
-
Control
- CSA:
-
Cross-sectional area
- d :
-
Cohn’s d
- EMG:
-
Electromyography
- ES:
-
Effect size
- ITT:
-
Interpolated twitch technique
- MFR:
-
Mean firing rate
- MVC:
-
Maximal voluntary contraction
- MU:
-
Motor unit
- MUAPAMPS :
-
Motor unit action potential amplitudes
- η p 2 :
-
Partial eta-squared
- PD:
-
Precision decomposition
- RET:
-
Resistance exercise training
- RF:
-
Rectus femoris
- RT:
-
Recruitment threshold
- ST:
-
Semitendinosus
- STA:
-
Spike trigger averaging
- sFAT:
-
Subcutaneous fat
- VL:
-
Vastus lateralis
- VM:
-
Vastus medialis
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Acknowledgements
We would like to acknowledge all children and parents for their time commitment to this study.
Funding
This study was funded by the National Strength and Conditioning Association Foundation.
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TH conceived and designed research. TH, EH, CC, KM, and AH conducted experiments. JT, RS, CC, and AH assisted in the development of the manuscript.
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Herda, T.J., Holmes, E.A., Cleary, C.J. et al. Motor unit firing rates increase in prepubescent youth following linear periodization resistance exercise training. Eur J Appl Physiol (2024). https://doi.org/10.1007/s00421-024-05455-w
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DOI: https://doi.org/10.1007/s00421-024-05455-w