Central fatigue assessment following high-intensity exercise performed in human dorsiflexor muscles

Background: Central fatigue (CF) is defined as a progressive exercise-induced failure in the voluntary activation (VA) of the muscle. Muscle afferent III and IV neurons are proposed to be major contributors to central fatigue development by detecting increases in intramuscular metabolite accumulation that leads to inhibition of descending neural drive during voluntary contractions. Yet, during high-intensity exercise, few studies show evidence of central fatigue using the interpolated twitch technique. These results contradict the current hypotheses regarding the inhibitory function of group III/IV afferents on the voluntary activation of muscles. Objective: 1) To develop a method to better evaluate central fatigue during high-intensity interval exercise (HIIE). 2) To investigate the proposed influence of group III/IV metabolite receptors on central fatigue development during HIIE. Hypothesis: It was hypothesized that voluntary activation failure would be evident following metabolically-demanding HIIE by assessing central fatigue during a 60 s sustained maximal effort contraction that stresses the neural activation of muscle. Methods: Ten healthy, recreationally active adult human participants (7 M; 3 F) performed six sets of 30 s all-out isokinetic concentric dorsiflexion at 160°/s. Each bout was followed by a 60 s sustained maximal voluntary contraction (MVC) whereby twitch interpolation was performed every 10 s during the MVC to measure voluntary activation. Each set was followed by a 2-min rest. Results: Minimal central fatigue was observed during the 60 s sustained MVC following each set of high-intensity interval exercise. Relative to the pre-exercise set, some voluntary activation failure was observed at the following sets and timepoints (VA%): Post set-1 at 20 s (93%, p <0.05), post set-3 at 0 s and 20 s (93% and 89%, respectively p <0.05), and post set-5 at 10 s (93%, p <0.05). Mean VA% at post-exercise sets 3 (92%, p <0.01), 5 (92%, p <0.001), and 6 (92%, p <0.05) revealed minimal voluntary activation failure following HIIE. Conclusion: Our study revealed that the human dorsiflexor muscles are resilient against central fatigue development during metabolically-demanding high-intensity exercise. Funded by NSERC Discovery and American Physiology Society SURF program. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.