Assessing Physiological Durability in Trail Runners: Terrain-Specific Responses to a 90-Minute Submaximal Run

Physiological durability-the ability to maintain physiological function during prolonged exercise-has been investigated in road runners but remains largely unexplored in trail running. Given the unique mechanical and energetic demands of uphill and downhill terrain, it is unclear how fatigue develops across different segments of a trail course. This study aimed to assess physiological deterioration and terrain-specific performance decline in recreational trail runners following a 90-minute submaximal effort.

Twenty-five recreational trail runners (4 females, V˙O2max: 54.6 [6.8] mL·kg-1·min-1) completed a time trial and treadmill-based cost-of-locomotion (CoL) test before and after a 90-minute trail run at 66% of the heart-rate range between lactate threshold and lactate turn point. Changes in CoL, ventilatory and cardiovascular variables, and time-trial performance on a 3.8-km outdoor course were analyzed.

Postfatigue time-trial completion time increased significantly (+7.7%), driven by slower uphill segments, whereas downhill segments remained unchanged. CoL and blood lactate did not differ postexercise. However, heart rate increased (+6.5%), oxygen pulse decreased (-7.8%), tidal volume declined (-13.9%), and breathing frequency increased (+19.9%) during the postfatigue CoL test, despite unchanged ventilation. During the prolonged run, progressive slowing of uphill segments occurred despite stable heart rate, indicating internal-external workload decoupling.

The prolonged effort induced terrain-specific performance decline and physiological strain despite preserved metabolic cost. These findings support the relevance of physiological durability in trail running and suggest that uphill fatigue may be a critical limiter in recreational athletes.