Central Fatigue Aetiology in Prolonged Trail Running Races.

Espeit, L; Brownstein, C G; Royer, N; Besson, T; Martin, V; Millet, G Y; Lapole, T

NEW FINDINGS What is the central question of this study? Are spinal and/or supraspinal perturbations implicated in central fatigue induced in the plantar flexor muscles following prolonged trail running races? What is the main finding and its importance? The present study confirmed the presence of central fatigue following various trail running distances from 40- to 170-km. The reduction in V-wave in conjunction with the lack of change in H-reflex suggests that a major component of this central fatigue may arise from supraspinal mechanisms in the plantar flexor muscles. ABSTRACT Trail running races are known to induce considerable impairments in neuromuscular function of which central mechanisms are a substantial component. However, the loci of this central fatigue (i.e. supraspinal and/or spinal) is not well identified. The aim of this study was to better understand central fatigue aetiology induced in the plantar flexor muscles by various trail running distances from 40- to 170-km. Eighteen runners participated in the study and neuromuscular function of their plantar flexors was tested before (PRE) and after (POST) various races during the Ultra-Trail du Mont Blanc. Neuromuscular function was evaluated with voluntary and evoked contractions using electrical tibial nerve stimulation. H-reflex and V-wave responses were also measured during submaximal and maximal voluntary contraction, respectively. Reductions in maximal voluntary contraction torque (-29%; p<0.001) and voluntary activation level (-12%; p<0.001) were observed after trail running races. V-wave was reduced in soleus (-35%; p = 0.003) and gastrocnemius medialis (-28%; p = 0.031), with no changes for H-reflex in soleus (p = 0.577). The present study confirmed the presence of central fatigue following trail running exercise. The reduction in V-wave in conjunction with the lack of change in H-reflex suggests that a major component of this central fatigue may arise from supraspinal mechanisms. This article is protected by copyright. All rights reserved.