Abstract
Neural and morphological adaptations determine gains of muscle strength. For youth athletes, the importance of morphological adaptation is typically highlighted based on the change in maturity status. However, the long-term development of neural components in youth athletes remains unclear. The present study investigated the longitudinal development of muscle strength, muscle thickness (MT), and motor unit firing activity of the knee extensor and their relationships in youth athletes. Seventy male youth soccer players (mean ± SD age = 16.3 ± 0.6 years) performed neuromuscular, maximal voluntary isometric contraction (MVC), and submaximal ramp contraction (at 30 and 50% MVC) tests with knee extensors, two times with a 10-month measurement interval. High-density surface electromyography was recorded from the vastus lateralis and decomposed to identify each individual motor unit activity. MT was evaluated by the sum of the vastus lateralis and vastus intermedius thicknesses. Finally, sixty-four participants were employed to compare MVC and MT, and 26 participants were employed to analyze motor unit activity. MVC and MT were increased from pre to post (p < 0.05, 6.9 and 1.7% for MVC and MT, respectively). Y-intercept of the regression line between median firing rate vs. recruitment threshold was also increased (p < 0.05, 13.3%). Multiple regression analysis demonstrated that the gains of both MT and Y-intercept were explanatory variables for the gain of strength. These findings suggest that the neural adaptation could also make the important contribution to the strength gain for the youth athletes over a 10-month training period.
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Data availability
Data that support the findings of the present study are presented in the text, figures and table, and are available from the corresponding author upon reasonable request.
Abbreviations
- HDsEMG:
-
High-density surface electromyography
- ICC:
-
Intraclass correlation coefficients
- LTAD:
-
Long-term athlete development
- MVC:
-
Maximal voluntary isometric contraction
- MT:
-
Muscle thickness
- PHV:
-
Peak height velocity
- PNR:
-
Pulse-to-noise ratio
- RMS:
-
Root mean square
- VL:
-
Vastus lateralis
- VI:
-
Vastus intermedius
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Acknowledgements
The authors would like to thank all participants. The authors also appreciate the contribution of Mr Kenji Yoshioka, Mr Takehisa Yamada, and Mr Yoshinori Arakawa of Nagoya Junior and Senior High School for helping our measurements and providing valuable comments in interpretation of the results.
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This study was supported by the Bilateral Program of JSPS (JPJSBP-82626) to KW and AH and by the Slovenian Research Agency (project J2-1731, L7-9421 and Program funding P2-0041) to AH.
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MO and KW contributed to the conception and design of the study. MO, TH, RT, TN, SU, and AY conducted experiments and acquired data. MO and AH performed analysis of the results. MO and KW contributed to interpretation of the results and revision of the manuscript. All authors have approved the final version of the submitted manuscript for publication. All designated authors qualify for authorship.
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Okudaira, M., Hirono, T., Takeda, R. et al. Longitudinal development of muscle strength and relationship with motor unit activity and muscle morphological characteristics in youth athletes. Exp Brain Res 241, 1009–1019 (2023). https://doi.org/10.1007/s00221-023-06590-0
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DOI: https://doi.org/10.1007/s00221-023-06590-0