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Modulations in motor unit discharge are related to changes in fascicle length during isometric contractions.
Martinez-Valdes, Eduardo; Negro, Francesco; Botter, Alberto; Pincheira, Patricio A; Cerone, Giacinto Luigi; Falla, Deborah; Lichtwark, Glen A; Cresswell, Andrew G.
Afiliación
  • Martinez-Valdes E; Centre of Precision Rehabilitation for Spinal Pain, School of Sport, Exercise and Rehabilitation Sciences, https://ror.org/03angcq70University of Birmingham, Birmingham, United Kingdom.
  • Negro F; Department of Clinical and Experimental Sciences, Università degli Studi di Brescia, Brescia, Italy.
  • Botter A; Laboratory for Engineering of the Neuromuscular System (LISiN), Department of Electronics and Telecommunication, Politecnico di Torino, Torino, Italy.
  • Pincheira PA; PoliToBIOMed Lab, Politecnico di Torino, Turin, Italy.
  • Cerone GL; School of Human Movement and Nutrition Sciences, The University of Queensland, Brisbane, Queensland, Australia.
  • Falla D; Laboratory for Engineering of the Neuromuscular System (LISiN), Department of Electronics and Telecommunication, Politecnico di Torino, Torino, Italy.
  • Lichtwark GA; PoliToBIOMed Lab, Politecnico di Torino, Turin, Italy.
  • Cresswell AG; Centre of Precision Rehabilitation for Spinal Pain, School of Sport, Exercise and Rehabilitation Sciences, https://ror.org/03angcq70University of Birmingham, Birmingham, United Kingdom.
J Appl Physiol (1985) ; 133(5): 1136-1148, 2022 Nov 01.
Article en En | MEDLINE | ID: mdl-36227169
The integration of electromyography (EMG) and ultrasound imaging has provided important information about the mechanisms of muscle activation and contraction. Unfortunately, conventional bipolar EMG does not allow an accurate assessment of the interplay between the neural drive received by muscles, changes in fascicle length and torque. We aimed to assess the relationship between modulations in tibialis anterior muscle (TA) motor unit (MU) discharge, fascicle length, and dorsiflexion torque using ultrasound-transparent high-density EMG electrodes. EMG and ultrasound images were recorded simultaneously from TA using a 32-electrode silicon matrix while performing isometric dorsiflexion contractions at two ankle joint positions (0° or 30° plantar flexion) and torques (20% or 40% of maximum). EMG signals were decomposed into MUs and changes in fascicle length were assessed with a fascicle-tracking algorithm. MU firings were converted into a cumulative spike train (CST) that was cross-correlated with torque (CST-torque) and fascicle length (CST-length). High cross-correlations were found for CST-length (0.60, range: 0.31-0.85) and CST-torque (0.71, range: 0.31-0.88). Cross-correlation delays revealed that the delay between CST-fascicle length (∼75 ms) was smaller than CST-torque (∼150 ms, P < 0.001). These delays affected MU recruitment and de-recruitment thresholds since the fascicle length at which MUs were recruited and de-recruited was similar but MU recruitment-de-recruitment torque varied. This study demonstrates that changes in TA fascicle length are related to modulations in MU firing and dorsiflexion torque. These relationships allow assessment of the interplay between neural drive, muscle contraction and torque, enabling the time required to convert neural activity into movement to be quantified.NEW & NOTEWORTHY By employing ultrasound-transparent high-density EMG electrodes, we show that modulations in tibialis anterior muscle motor unit discharge rate were related to both changes in fascicle length and resultant torque. These relationships permitted the quantification of the relative delays between fluctuations in neural drive, muscle contraction, and transfer of torque via the tendon during sustained isometric dorsiflexion contractions, providing information on the conversion of neural activity into muscle force during a contraction.
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Texto completo: 1 Colección: 01-internacional Base de datos: MEDLINE Asunto principal: Alta del Paciente / Contracción Isométrica Límite: Humans Idioma: En Revista: J Appl Physiol (1985) Asunto de la revista: FISIOLOGIA Año: 2022 Tipo del documento: Article País de afiliación: Reino Unido Pais de publicación: Estados Unidos

Texto completo: 1 Colección: 01-internacional Base de datos: MEDLINE Asunto principal: Alta del Paciente / Contracción Isométrica Límite: Humans Idioma: En Revista: J Appl Physiol (1985) Asunto de la revista: FISIOLOGIA Año: 2022 Tipo del documento: Article País de afiliación: Reino Unido Pais de publicación: Estados Unidos