Neural and muscular determinants of maximal rate of force development

Jakob Lund Dideriksen, Alessandro Del Vecchio, Dario Farina

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

The ability to produce rapid forces requires quick motor unit recruitment, high motor unit discharge rates, and fast motor unit force twitches. The relative importance of these parameters for maximum rate of force development (RFD), however, is poorly understood. In this study, we systematically investigated these relations using a computational model of motor unit pool activity and force. Across simulations, neural and muscular properties were systematically varied in experimentally observed ranges. Motor units were recruited over an interval starting from contraction onset (range: 22-233 ms). Upon recruitment, discharge rates declined from an initial rate (range: 89-212 pps) with varying likelihood of doublet (inter-spike interval of 3 ms; range: 0-50%). Finally, muscular adaptations were modeled by changing average twitch contraction time (range: 42-78 ms). Spectral analysis showed that the effective neural drive to the simulated muscle had smaller bandwidths than the average motor unit twitch indicating that the bandwidth of the motor output, and thus the capacity for explosive force, was limited mainly by neural properties. The simulated RFD increased by 1,050 ± 281 %MVC/s from the longest to the shortest recruitment interval. This effect was >4-fold higher than the effect of increasing the initial discharge rate, >5-fold higher than the effect of increasing the chance of doublets, and >6-fold higher than the effect of decreasing twitch contraction times. The simulated results suggest that the physiological variation of the rate by which motor units are recruited during ballistic contractions is the main determinant for the variability in RFD across individuals.

Original languageEnglish
JournalJournal of Neurophysiology
ISSN0022-3077
DOIs
Publication statusAccepted/In press - 16 Oct 2019

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Neurophysiological Recruitment
Muscles

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title = "Neural and muscular determinants of maximal rate of force development",
abstract = "The ability to produce rapid forces requires quick motor unit recruitment, high motor unit discharge rates, and fast motor unit force twitches. The relative importance of these parameters for maximum rate of force development (RFD), however, is poorly understood. In this study, we systematically investigated these relations using a computational model of motor unit pool activity and force. Across simulations, neural and muscular properties were systematically varied in experimentally observed ranges. Motor units were recruited over an interval starting from contraction onset (range: 22-233 ms). Upon recruitment, discharge rates declined from an initial rate (range: 89-212 pps) with varying likelihood of doublet (inter-spike interval of 3 ms; range: 0-50{\%}). Finally, muscular adaptations were modeled by changing average twitch contraction time (range: 42-78 ms). Spectral analysis showed that the effective neural drive to the simulated muscle had smaller bandwidths than the average motor unit twitch indicating that the bandwidth of the motor output, and thus the capacity for explosive force, was limited mainly by neural properties. The simulated RFD increased by 1,050 ± 281 {\%}MVC/s from the longest to the shortest recruitment interval. This effect was >4-fold higher than the effect of increasing the initial discharge rate, >5-fold higher than the effect of increasing the chance of doublets, and >6-fold higher than the effect of decreasing twitch contraction times. The simulated results suggest that the physiological variation of the rate by which motor units are recruited during ballistic contractions is the main determinant for the variability in RFD across individuals.",
author = "Dideriksen, {Jakob Lund} and {Del Vecchio}, Alessandro and Dario Farina",
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day = "16",
doi = "10.1152/jn.00330.2019",
language = "English",
journal = "Journal of Neurophysiology",
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Neural and muscular determinants of maximal rate of force development. / Dideriksen, Jakob Lund; Del Vecchio, Alessandro; Farina, Dario.

In: Journal of Neurophysiology, 16.10.2019.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - Neural and muscular determinants of maximal rate of force development

AU - Dideriksen, Jakob Lund

AU - Del Vecchio, Alessandro

AU - Farina, Dario

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N2 - The ability to produce rapid forces requires quick motor unit recruitment, high motor unit discharge rates, and fast motor unit force twitches. The relative importance of these parameters for maximum rate of force development (RFD), however, is poorly understood. In this study, we systematically investigated these relations using a computational model of motor unit pool activity and force. Across simulations, neural and muscular properties were systematically varied in experimentally observed ranges. Motor units were recruited over an interval starting from contraction onset (range: 22-233 ms). Upon recruitment, discharge rates declined from an initial rate (range: 89-212 pps) with varying likelihood of doublet (inter-spike interval of 3 ms; range: 0-50%). Finally, muscular adaptations were modeled by changing average twitch contraction time (range: 42-78 ms). Spectral analysis showed that the effective neural drive to the simulated muscle had smaller bandwidths than the average motor unit twitch indicating that the bandwidth of the motor output, and thus the capacity for explosive force, was limited mainly by neural properties. The simulated RFD increased by 1,050 ± 281 %MVC/s from the longest to the shortest recruitment interval. This effect was >4-fold higher than the effect of increasing the initial discharge rate, >5-fold higher than the effect of increasing the chance of doublets, and >6-fold higher than the effect of decreasing twitch contraction times. The simulated results suggest that the physiological variation of the rate by which motor units are recruited during ballistic contractions is the main determinant for the variability in RFD across individuals.

AB - The ability to produce rapid forces requires quick motor unit recruitment, high motor unit discharge rates, and fast motor unit force twitches. The relative importance of these parameters for maximum rate of force development (RFD), however, is poorly understood. In this study, we systematically investigated these relations using a computational model of motor unit pool activity and force. Across simulations, neural and muscular properties were systematically varied in experimentally observed ranges. Motor units were recruited over an interval starting from contraction onset (range: 22-233 ms). Upon recruitment, discharge rates declined from an initial rate (range: 89-212 pps) with varying likelihood of doublet (inter-spike interval of 3 ms; range: 0-50%). Finally, muscular adaptations were modeled by changing average twitch contraction time (range: 42-78 ms). Spectral analysis showed that the effective neural drive to the simulated muscle had smaller bandwidths than the average motor unit twitch indicating that the bandwidth of the motor output, and thus the capacity for explosive force, was limited mainly by neural properties. The simulated RFD increased by 1,050 ± 281 %MVC/s from the longest to the shortest recruitment interval. This effect was >4-fold higher than the effect of increasing the initial discharge rate, >5-fold higher than the effect of increasing the chance of doublets, and >6-fold higher than the effect of decreasing twitch contraction times. The simulated results suggest that the physiological variation of the rate by which motor units are recruited during ballistic contractions is the main determinant for the variability in RFD across individuals.

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JO - Journal of Neurophysiology

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