Contraction speed influence the neural activation of m. Tibialis Anterior during submaximal dynamic contractions
Authors
Christensen, Anders Juul ; Kristoffersen, Simon Spanggaard
Term
4. semester
Education
Publication year
2020
Submitted on
2020-06-02
Pages
15
Abstract
Denne afhandling undersøger, hvordan kontraktionshastighed påvirker den neurale aktivering af m. tibialis anterior under submaksimale dynamiske dorsalfleksioner. Formålet var at analysere både EMG-amplituden og den rumlige fordeling af aktivitet (RMS-barycenter) på tværs af kontraktionstyper (koncentrisk og ekscentrisk) og forskellige muskelpositioner. Elleve raske mænd udførte dorsalfleksioner i et dynamometer ved to hastigheder (5°/s og 20°/s) og to intensiteter (10% og 25% af MVC), mens aktivitet blev registreret med to 64-kanals HD-sEMG-matricer. RMS blev normaliseret til den isometriske fase, barycenteret blev fulgt gennem bevægelsen, og data blev analyseret med trevej-ANOVA. Resultaterne viste, at ved 25% af MVC var EMG-amplituden forskellig mellem hastigheder, og interaktionen mellem hastighed og kontraktionstype var signifikant, mens dette ikke sås ved 10%. Interaktionen mellem muskelposition og hastighed var signifikant ved begge intensiteter. Barycenteret ændrede sig med muskelposition ved både 10% og 25% og med kontraktionstype ved 10%, men hastighed ændrede ikke den rumlige fordeling af aktivitet. Samlet tyder fundene på, at øget hastighed påvirker neural rekruttering afhængigt af bevægeudslag og kontraktionstype, mens det overordnede rumlige rekrutteringsmønster bevares; desuden kræver en mere længdeudspændt muskel lavere rekruttering ved lav hastighed.
This thesis examines how contraction speed influences neural activation of the tibialis anterior during submaximal dynamic ankle dorsiflexion. The aim was to assess both EMG amplitude and the spatial distribution of activity (RMS barycenter) across contraction types (concentric and eccentric) and different muscle positions. Eleven healthy men performed dorsiflexion in a dynamometer at two speeds (5°/s and 20°/s) and two intensities (10% and 25% of MVC), while activity was recorded using two 64-channel high-density sEMG arrays. RMS was normalized to the isometric phase, the barycenter was tracked throughout the movement, and data were analyzed with a three-way ANOVA. Results showed that at 25% MVC, EMG amplitude differed between speeds, and the interaction between speed and contraction type was significant, whereas this was not observed at 10%. The interaction between muscle position and speed was significant at both intensities. The barycenter varied with muscle position at both 10% and 25%, and with contraction type at 10%, but speed did not alter the spatial distribution of activity. Overall, the findings indicate that higher contraction speed affects neural recruitment depending on range of motion and contraction type, while the spatial recruitment pattern is preserved; additionally, a more lengthened muscle requires lower recruitment at low speed.
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