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Title: 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
Authors: Del Vecchio, Alessandro
Negro, Francesco
Holobar, Ales
Casolo, Andrea
Folland, Jonathan P.
Felici, Francesco
Farina, Dario
Keywords: Motor unit
Neural Drive
Spike frequency adaptation
Ballistic contractions
EMG Decomposition
Issue Date: 2019
Publisher: Wiley © The Authors, The Journal of Physiology, The Physiological Society
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.
Abstract: 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.
Description: This paper is closed access until 1 March 2020.
Sponsor: 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).
Version: Accepted for publication
DOI: 10.1113/JP277396
URI: https://dspace.lboro.ac.uk/2134/37673
Publisher Link: https://doi.org/10.1113/JP277396
ISSN: 0022-3751
Appears in Collections:Closed Access (Sport, Exercise and Health Sciences)

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