In Medicine and science in sports and exercise
PURPOSE : Adjustments in motor unit (MU) discharge properties have been shown following short-term resistance training, however MU adaptations in long-term resistance-trained individuals are less clear. Here, we concurrently assessed MU discharge characteristics and MU conduction velocity in long-term resistance-trained (RT) and untrained (UT) men.
METHODS : MU 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 medialis (VM) of RT (>3 years; N = 14) and UT (N = 13) during submaximal and maximal isometric knee extension.
RESULTS : RT were on average 42% stronger (maximal voluntary force, MVF: 976.7 ± 85.4 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 vs. 10.3 ± 1.5 pps, VM: 10.7 ± 1.6 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 to UT (VL: 21.1 ± 4.1 vs. 14.0 ± 4.5 pps, VM: 19.5 ± 5.0 vs. 17.0 ± 6.3 pps; p = 0.7173). MU conduction velocity was greater in RT compared to UT individuals in both VL (4.9 ± 0.5 vs. 4.5 ± 0.3 m.s-1; p < 0.0013) and VM (4.8 ± 0.5 vs. 4.4 ± 0.3 m.s-1; p < 0.0073).
CONCLUSIONS : RT and UT 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.
Škarabot Jakob, Folland Jonathan P, Forsyth Jules, Vazoukis Apostolos, Holobar Aleš, Del Vecchio Alessandro
2022-Dec-22
