Motor Unit Firing Rates Increase in Prepubescent Youth Following Linear Periodization Resistance Exercise Training

Overview

Journal Eur J Appl Physiol

Specialty Physiology

Date 2024 Apr 18

PMID 38634901

Authors

Trent J Herda

Elizabeth A Holmes

Christopher J Cleary

Kelsey T Minor

John P Thyfault

Robin P Shook

Ashley A Herda

Affiliations

Soon will be listed here.

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.

References

Beck T . The importance of a priori sample size estimation in strength and conditioning research. J Strength Cond Res. 2013; 27(8):2323-37. DOI: 10.1519/JSC.0b013e318278eea0. View

Behm D, Faigenbaum A, Falk B, Klentrou P . Canadian Society for Exercise Physiology position paper: resistance training in children and adolescents. Appl Physiol Nutr Metab. 2008; 33(3):547-61. DOI: 10.1139/H08-020. View

Bull F, Al-Ansari S, Biddle S, Borodulin K, Buman M, Cardon G . World Health Organization 2020 guidelines on physical activity and sedentary behaviour. Br J Sports Med. 2020; 54(24):1451-1462. PMC: 7719906. DOI: 10.1136/bjsports-2020-102955. View

Burke R, Rudomin P, Zajac 3rd F . Catch property in single mammalian motor units. Science. 1970; 168(3927):122-4. DOI: 10.1126/science.168.3927.122. View

Button D, Behm D . The effect of stimulus anticipation on the interpolated twitch technique. J Sports Sci Med. 2013; 7(4):520-4. PMC: 3761925. View

De Luca C, Adam A, Wotiz R, Gilmore L, Nawab S . Decomposition of surface EMG signals. J Neurophysiol. 2006; 96(3):1646-57. DOI: 10.1152/jn.00009.2006. View

DeFronzo R, Jacot E, Jequier E, MAEDER E, Wahren J, Felber J . The effect of insulin on the disposal of intravenous glucose. Results from indirect calorimetry and hepatic and femoral venous catheterization. Diabetes. 1981; 30(12):1000-7. DOI: 10.2337/diab.30.12.1000. View

Dotan R, Mitchell C, Cohen R, Klentrou P, Gabriel D, Falk B . Child-adult differences in muscle activation--a review. Pediatr Exerc Sci. 2012; 24(1):2-21. PMC: 3804466. DOI: 10.1123/pes.24.1.2. View

Enoka R, Duchateau J . Rate Coding and the Control of Muscle Force. Cold Spring Harb Perspect Med. 2017; 7(10). PMC: 5629984. DOI: 10.1101/cshperspect.a029702. View

10.

Faigenbaum A, Kraemer W, Blimkie C, Jeffreys I, Micheli L, Nitka M . Youth resistance training: updated position statement paper from the national strength and conditioning association. J Strength Cond Res. 2009; 23(5 Suppl):S60-79. DOI: 10.1519/JSC.0b013e31819df407. View

11.

Falk B . Resistance training in children. Pediatr Exerc Sci. 2015; 27(1):13-7. DOI: 10.1123/pes.2015-0028. View

12.

Farina D, Merletti R, Enoka R . The extraction of neural strategies from the surface EMG: an update. J Appl Physiol (1985). 2014; 117(11):1215-30. PMC: 4254845. DOI: 10.1152/japplphysiol.00162.2014. View

13.

Fuglevand A, Lester R, Johns R . Distinguishing intrinsic from extrinsic factors underlying firing rate saturation in human motor units. J Neurophysiol. 2014; 113(5):1310-22. PMC: 4346713. DOI: 10.1152/jn.00777.2014. View

14.

Fukunaga T, Funato K, Ikegawa S . The effects of resistance training on muscle area and strength in prepubescent age. Ann Physiol Anthropol. 1992; 11(3):357-64. DOI: 10.2114/ahs1983.11.357. View

15.

Gillen Z, Housh T, Schmidt R, Herda T, De Ayala R, Shoemaker M . Comparisons of muscle strength, size, and voluntary activation in pre- and post-pubescent males and females. Eur J Appl Physiol. 2021; 121(9):2487-2497. DOI: 10.1007/s00421-021-04717-1. View

16.

Herbert R, Gandevia S . Twitch interpolation in human muscles: mechanisms and implications for measurement of voluntary activation. J Neurophysiol. 1999; 82(5):2271-83. DOI: 10.1152/jn.1999.82.5.2271. View

17.

Herda T . Resistance exercise training and the motor unit. Eur J Appl Physiol. 2022; 122(9):2019-2035. DOI: 10.1007/s00421-022-04983-7. View

18.

Herda T, Ryan E, Kohlmeier M, Trevino M, Gerstner G, Roelofs E . Examination of muscle morphology and neuromuscular function in normal weight and overfat children aged 7-10 years. Scand J Med Sci Sports. 2018; 28(11):2310-2321. DOI: 10.1111/sms.13256. View

19.

Herda T, Gallagher P, Miller J, Bubak M, Parra M . Skeletal Muscle Composition and Glucose Levels in Children Who Are Overweight and Obese. Pediatr Exerc Sci. 2020; 32(3):157-164. DOI: 10.1123/pes.2020-0018. View

20.

Herda T, Parra M, Miller J, Sterczala A, Kelly M . Measuring the accuracies of motor unit firing times and action potential waveforms derived from surface electromyographic decomposition. J Electromyogr Kinesiol. 2020; 52:102421. DOI: 10.1016/j.jelekin.2020.102421. View