Motor Unit Discharge Characteristics and Conduction Velocity of the Vastii Muscles in Long-Term Resistance-Trained Men

Author:

ŠKARABOT JAKOB1,FOLLAND JONATHAN P.,FORSYTH JULES1,VAZOUKIS APOSTOLOS1,HOLOBAR ALEŠ2,DEL VECCHIO ALESSANDRO3

Affiliation:

1. School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, UNITED KINGDOM

2. Systems Software Laboratory, Faculty of Electrical Engineering and Computer Science, University of Maribor, Maribor, SLOVENIA

3. Department Artificial Intelligence in Biomedical Engineering, Faculty of Engineering, Friedrich Alexander University, Erlangen-Nuremberg, GERMANY

Abstract

ABSTRACTPurposeAdjustments in motor unit (MU) discharge properties have been shown after short-term resistance training; however, MU adaptations in long-term resistance-trained (RT) individuals are less clear. Here, we concurrently assessed MU discharge characteristics and MU conduction velocity in long-term RT and untrained (UT) men.MethodsMotor unit discharge characteristics (discharge rate, recruitment, and derecruitment threshold) and MU conduction velocity were assessed after the decomposition of high-density electromyograms recorded from vastus lateralis (VL) and vastus medialis (VM) of RT (>3 yr;n= 14) and UT (n= 13) during submaximal and maximal isometric knee extension.ResultsResistance-trained men were on average 42% stronger (maximal voluntary force [MVF], 976.7 ± 85.4 N vs 685.5 ± 123.1 N;P< 0.0001), but exhibited similar relative MU recruitment (VL, 21.3% ± 4.3% vs 21.0% ± 2.3% MVF; VM, 24.5% ± 4.2% vs 22.7% ± 5.3% MVF) and derecruitment thresholds (VL, 20.3% ± 4.3% vs 19.8% ± 2.9% MVF; VM, 24.2% ± 4.8% vs 22.9% ± 3.7% MVF;P≥ 0.4543). There were also no differences between groups in MU discharge rate at recruitment and derecruitment or at the plateau phase of submaximal contractions (VL, 10.6 ± 1.2 pps vs 10.3 ± 1.5 pps; VM, 10.7 ± 1.6 pps vs 10.8 ± 1.7 pps;P≥ 0.3028). During maximal contractions of a subsample population (10 RT, 9 UT), MU discharge rate was also similar in RT compared with UT (VL, 21.1 ± 4.1 pps vs 14.0 ± 4.5 pps; VM, 19.5 ± 5.0 pps vs 17.0 ± 6.3 pps;P= 0.7173). Motor unit conduction velocity was greater in RT compared with UT individuals in both VL (4.9 ± 0.5 m·s−1vs 4.5 ± 0.3 m·s−1;P< 0.0013) and VM (4.8 ± 0.5 m·s−1vs 4.4 ± 0.3 m·s−1;P< 0.0073).ConclusionsResistance-trained and UT men display similar MU discharge characteristics in the knee extensor muscles during maximal and submaximal contractions. The between-group strength difference is likely explained by superior muscle morphology of RT as suggested by greater MU conduction velocity.

Publisher

Ovid Technologies (Wolters Kluwer Health)

Subject

Physical Therapy, Sports Therapy and Rehabilitation,Orthopedics and Sports Medicine

Reference63 articles.

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