Neuromuscular Fatigue and Perceived Fatigability in the Hours Following a High-Intensity Endurance Running Depend on the Exercise Protocol.

This study investigated neuromuscular fatigue and perceived fatigability across different high-intensity endurance running protocols. Twelve males (mean ± SD; V ˙ O 2 max : 52.2 ± 6.9 mL/kg/min) ran ∼8.0 km: (i) at the velocity associated to the respiratory compensation point (vRCP; 5 × 8 min bouts ‒ RUN100%RCP); (ii) at 30% above vRCP (10 × 3 min bouts ‒ RUN130%RCP); and (iii) at 50% above vRCP (20 × 80 s bouts ‒ RUN150%RCP). Before and for 6 h post-exercise, voluntary and evoked contractions of knee-extensors were assessed, alongside tiredness, leg pain, and perceived recovery. Following all protocols, voluntary activation remained depressed for up to 4 h post-exercise, while voluntary peak force was reduced for at least 6 h (p < 0.05). Other neuromuscular function markers reduced (p < 0.05) according to the protocol. No time × protocol interaction was observed for any neuromuscular function marker (p > 0.05). Aggregate data (protocol effect, p < 0.05) evidenced greater reduction in neural drive to vastus lateralis (RMSVL/Mwamp) after RUN100%RCP (-20%) compared to RUN130%RCP (-3%) and RUN150%RCP (-7%); and greater reduction in late rate of force development (RFD; 100-200 ms) and contractile function (Qtwpot) after RUN150%RCP (-18% and -8%, respectively) than RUN100%RCP (-8% and -2%, respectively). Leg pain and tiredness remained elevated (p < 0.05) for at least 6 h following all protocols. Leg pain and tiredness were greater for up to 4 h and for at least 6 h, respectively, after RUN150%RCP than RUN100%RCP (time × protocol interaction; p < 0.05). The choice of exercise protocol influences the extent of reduction in vastus lateralis neural drive, impairments in knee-extensors contractile function, and perceived fatigability for hours following a high-intensity endurance running.