Neuromuscular fatigability amplitude and aetiology are interrelated across muscles

Abstract

New findings: What is the central question of this study? Is neuromuscular fatigability interrelated between different muscle groups from the same individual during isometric all-out exercise? What is the main finding and its importance? Although the average decrease can vary between muscles, an individual demonstrates interrelated fatigability aetiology regardless of the muscle group tested. The inter-individual variability provides evidence of different profiles common between muscles, which can be regarded as an individual characteristic.

Abstract: Neuromuscular fatigability is commonly attributed to central and peripheral origins. However, there is strong evidence of interactions between these two mechanisms. According to the idea that peripheral fatigability might be centrally regulated, one can hypothesize that neuromuscular fatigability would be correlated between different muscle groups at the individual level. Thirty-two healthy participants (16 women and 16 men) completed two 5 min fatiguing exercises [60 isometric maximal voluntary contractions (MVCs)] with finger flexors (FFs) and ankle plantar flexors (PFs) in two randomized sessions. Neuromuscular testing was conducted before, during (every six MVCs) and directly after the fatigue procedure. The force asymptote (F_A ) was calculated as the asymptote of the force-time relationship. Changes (post- vs. pre-fatigue) in the exercise-evoked force (ΔDb₁₀₀ ), voluntary activation (ΔVA) and central activation ratio (∆CAR) were also investigated. Significant correlations were found between FFs and PFs for F_A , ΔDb₁₀₀ and ΔVA (r = 0.65, r = 0.63 and r = 0.50, respectively). A significant negative correlation between ∆CAR and ∆Db₁₀₀ was evidenced for both PFs (r = -0.82) and FFs (r = -0.57). Neuromuscular fatigability is correlated between different muscle groups at the individual level. The results support the idea that a restrained motor drive prevents large peripheral perturbations and that individuals exhibit correlated fatigability aetiology regardless of the muscle group tested. Widely different central/peripheral profiles can be found amongst individuals, and a part of the fatigability aetiology can be regarded as an individual characteristic.

Keywords: fatigability origin; force-time asymptote; intermuscle comparison.