Trail-Running Durability During Race Simulation at Moderate Altitude (1850 m): Speed Decline, Force Loss, and Ventilatory Adjustments Without Increased Energy Cost in Well-Trained Runners.

BACKGROUND: Durability, defined as the progressive deterioration in performance (eg, speed or power output) during prolonged exercise, remains underexplored in trail running particularly under race-like conditions. The underlying physiological mechanisms contributing to this deterioration are increasingly described as resilience. This study investigated neuromuscular, ventilatory, and pacing responses during a simulated trail running race in well-trained athletes. METHODS: Sixteen trained male trail runners (V˙O2peak: 65.3 [7.4] mL·kg-1·min-1 at an altitude of 1850 m) completed 6 laps of a 3.6-km outdoor circuit (110-m elevation gain per lap). Participants were instructed to run as if in competition, aiming for maximal sustainable pace. Quadriceps maximal voluntary isometric contraction was assessed before (Pre), mid-race (Mid), and after the run (Post). Energetic cost of running (Cr), ventilatory, and cardiovascular variables were measured Pre and Post. RESULTS: Maximal voluntary isometric contraction declined progressively from Pre to Mid and Post (P < .001), indicating marked neuromuscular fatigue. Running speed decreased across laps (P < .001), reflecting impaired performance durability. Cr, measured 30-minute after the exercise, remained unchanged (P > .05), but ventilatory patterns were significantly altered: breathing frequency and minute ventilation increased, tidal volume decreased, and respiratory exchange ratio was reduced (all P < .05). CONCLUSION: Simulated trail racing induced substantial neuromuscular fatigue, pacing decline, and altered ventilatory and cardiovascular responses, even without increased metabolic cost. These findings highlight the multidimensional nature of durability in trail running and suggest that impairments in physiological resilience may occur independently of metabolic changes. Integrating additional markers such as breathing frequency could enhance training and monitoring strategies for trail athletes.