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You are as fast as your motor neurons: speed of recruitment and maximal discharge of motor neurons determine the maximal rate of force development in humans

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journal contribution
posted on 29.04.2019, 12:37 authored by Alessandro Del Vecchio, Francesco Negro, Ales Holobar, Andrea Casolo, Jonathan FollandJonathan Folland, Francesco Felici, Dario Farina
During rapid contractions, motor neurons are recruited in a short burst and begin to discharge at high frequencies (up to >200 Hz). In the present study, we investigated the behaviour of relatively large populations of motor neurons during rapid (explosive) contractions in humans, applying a new approach to accurately identify motor neuron activity simultaneous to measuring the rate of force development. The activity of spinal motor neurons was assessed by high-density electromyographic decomposition from the tibialis anterior muscle of 20 men during isometric explosive contractions. The speed of motor neuron recruitment and the instantaneous motor unit discharge rate were analysed as a function of the impulse (the time–force integral) and the maximal rate of force development. The peak of motor unit discharge rate occurred before force generation and discharge rates decreased thereafter. The maximal motor unit discharge rate was associated with the explosive force variables, at the whole population level (r 2  = 0.71 ± 0.12; P < 0.001). Moreover, the peak motor unit discharge and maximal rate of force variables were correlated with an estimate of the supraspinal drive, which was measured as the speed of motor unit recruitment before the generation of afferent feedback (P < 0.05). We show for the first time the full association between the effective neural drive to the muscle and human maximal rate of force development. The results obtained in the present study indicate that the variability in the maximal contractile explosive force of the human tibialis anterior muscle is determined by the neural activation preceding force generation.

Funding

This work was funded by Proof-of-Concept Project Inter-spine (737570) and the Slovenian Research Agency (project J2-7357 – Exact quantification of muscle control strategies and coactivation patterns in robot-assisted rehabilitation of hemi-paretic patients, and Programme funding P2-0041). F. Negro was funded by the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 702491 (NeuralCon).

History

School

  • Sport, Exercise and Health Sciences

Published in

The Journal of Physiology

Volume

597

Issue

9

Pages

2445 - 2456

Citation

DEL VECCHIO, A. ... et al, 2019. You are as fast as your motor neurons: speed of recruitment and maximal discharge of motor neurons determine the maximal rate of force development in humans. The Journal of Physiology, 597 (9), pp.2445-2456.

Publisher

Wiley © The Authors, The Journal of Physiology, The Physiological Society

Version

AM (Accepted Manuscript)

Publisher statement

This is the peer reviewed version of the following article: DEL VECCHIO, A. ... et al, 2019. You are as fast as your motor neurons: speed of recruitment and maximal discharge of motor neurons determine the maximal rate of force development in humans. The Journal of Physiology, 597 (9), pp.2445-2456, which has been published in final form at https://doi.org/10.1113/JP277396. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.

Acceptance date

04/02/2019

Publication date

2019-03-01

ISSN

0022-3751

eISSN

1469-7793

Language

en