Corticospinal and motor unit adaptations to rapid isometric strength training

Dawson Kidgell, Alan Pearce

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Abstract

Introduction: Modulation of the corticospinal pathway (CSP) has been suggested to contribute to the rapid development of strength during the first 4–6 weeks of strength training (ST). However, the exact role of the CSP in regulating neural adaptations is unclear. Since CSP inputs are important for motor unit (MU) recruitment, the purpose of this study was to determine the effect of rapid isometric strength training on motor unit discharge rate, synchronisation, corticospinal excitability and inhibition. Method: 16 subjects (24.1 ± 5.0 years) participated in the study and were randomly allocated into either ST or control group (C). ST subjects (n = 8) completed 12 supervised ST sessions over 4 weeks that involved 6 sets of 10 repetitions of an index finger abduction task for the right first dorsal interosseous (FDI) muscle only. Isometric Strength testing (maximum voluntary contraction, MVC) of the FDI, cross-correlation analysis and mean geometric discharge rate from single motor units and Transcranial Magnetic Stimulation (TMS) at 20% MVC were obtained prior to and following training. Corticospinal parameters of MT, motor evoked potential amplitude (MEP), and Electromyographic silent period duration (EMG SP) were obtained prior to and following training. Results: There was a 34% increase in strength of the trained right FDI (p = .001). There was no change within the control group. ST did not affect the strength of motor unit synchronisation or mean geometric discharge rate. There were no differences in CSP excitability, however, there was a significant reduction in CSP inhibition (SP duration) (p = .03). Discussion: The findings demonstrate, at least in a hand muscle, that rapid isometric strength training increases strength as a result of reduced inhibition within the CSP and not as a result of alterations in motor unit synchronistaion and discharge rate. Conclusion: Rapid isometric strength training reduces CSP inhibition, but has no effect on correlated motor unit activity, suggesting that reduced inhibition is important for the expression of strength.
Original languageEnglish
Pages (from-to)e25-e26
Number of pages2
JournalJournal of Science and Medicine in Sport
Volume13
Issue numberS1
DOIs
Publication statusPublished - Dec 2010
Externally publishedYes
EventASICS Conference of Science and Medicine in Sport 2010 - Port Douglas, Port Douglas, Australia
Duration: 3 Nov 20106 Nov 2010

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