Acute adaptation of central and peripheralmotor unit features to exercise-induced fatigue differs with concentric and eccentric loading

Jones J Eleanor, Yuxiao Guo, Eduardo Martinez Valdes, Francesco Negro, Daniel Stashuk, Philip Atherton, Bethan E Phillips, Mathew Piasecki*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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Abstract

Force output of muscle is partly mediated by the adjustment of motor unit (MU)
firing rate (FR). Disparities in MU features in response to fatigue may be influenced by contraction type, as concentric (CON) and eccentric (ECC) contractions demand variable amounts of neural input,which alters the response to fatigue. This study aimed to determine the effects of fatigue following CON and ECC loading on MU features of the vastus lateralis (VL). High-density surface (HD-sEMG) and intramuscular (iEMG) electromyography were used to record MU potentials (MUPs) from bilateral VLs of 12 young volunteers (six females) during sustained isometric contractions at 25% and 40% of the maximum voluntary contraction (MVC), before and after completing CON and ECC weighted stepping exercise. Multi-level mixed effects linear regression models were performed with significance assumed as P < 0.05. MVC decreased in both CON and ECC legs post-exercise (P < 0.0001), as did force steadiness at both 25% and 40% MVC (P < 0.004). MU FR increased in ECC at both contraction levels (P < 0.001) but did not change in CON. FR variability increased in both legs at 25% and 40%MVC following fatigue (P < 0.01). From iEMG measures at 25%MVC, MUP shape
did not change (P > 0.1) but neuromuscular junction transmission instability increased in both legs (P < 0.04), and markers of fibre membrane excitability increased following CON only (P = 0.018). These data demonstrate that central and peripheral MU features are altered following exercise-induced fatigue and differ according to exercise modality. This is important when considering interventional strategies targeting MU function.
Original languageEnglish
Pages (from-to)827-837
Number of pages11
JournalExperimental Physiology
Volume108
Issue number6
Early online date5 Apr 2023
DOIs
Publication statusPublished - 1 Jun 2023

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