Changes in motor unit conduction velocity after unilaterallower-limb suspension and active recovery are correlated withmuscle ion channel gene expression

Résumé fourni par la source

The effects of muscle disuse on the propagation of action potentials along motorunit (MU) muscle fibres, a key process for effective muscle activation and forcegeneration, remain poorly understood. The aim of this study was to investigate changesin action potential propagation and to identify biological factors influencing thesechanges following unilateral lower-limb suspension (ULLS) and active recovery (AR).Eleven young males underwent 10 days of ULLS followed by 21 days of AR involvingresistance exercise. Maximal force of the knee extensors (MVC), high-density surfaceEMG recordings and muscle biopsies of the vastus lateralis muscle were collectedbefore ULLS, after ULLS and after AR. EMG recordings collected during submaximalisometric contractions were decomposed to estimate single-MU conduction velocity(CV). Biopsies were used to measure muscle fibre diameters via histochemical analysisand ion channel transcriptomic profiles via mRNA sequencing. The MVC declined by29% after ULLS and returned to baseline after AR. MU CV decreased after ULLSand recovered fully, even exceeding baseline values after AR. Muscle fibre diametersdid not change across the interventions and showed no correlation with MU CV.Conversely, a feature importance analysis revealed that mRNA expression levels ofspecific ion channel genes, particularly those involved in K+ transport, were correlatedwith MU CV at baseline and across the interventions. This study highlights the crucialrole of K+ ion channels in influencing MU CV in humans, offering new insights into MUCV modulation and the mechanisms of changes in muscle force after disuse and activerecovery.

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