Author(s): JAEN-CARRILLO, D., BRUCE, C., GOBBO, C., HOWE, C., LAWLEY, J., Institution: UNIVERSITÄT INNSBRUCK, Country: AUSTRIA, Abstract-ID: 606

INTRODUCTION:
Endurance performance is classically explained by V̇O2max, fractional utilization, and running economy. Durability, the resistance to fatigue-induced drifts, has emerged as a fourth dimension. While durability research has focused on physiological responses, RE is also strongly influenced by biomechanics. Prolonged running alters spatiotemporal variables (e.g., ground contact time, duty factor), potentially affecting performance. Trail running involves prolonged subthreshold running interspersed with high-intensity uphill efforts, yet the integrated physiological and biomechanical durability under controlled intensity and nutrition remains unclear. This study examined durability in trained trail runners during prolonged subthreshold running with repeated uphill time trials.
METHODS:
Twenty-three trained trail runners completed: (i) a graded test to determine lactate threshold (LT); (ii) a 12-min uphill time trial (CON); and (iii) a 180-min treadmill run at 85% of LT+0.5 mmol·L⁻¹ with three 12-min uphill time trials every 60 min. Gas exchange, heart rate, blood lactate, RPE, substrate oxidation, and gait variables (cadence, stride length, ground contact time [GCT], duty factor [DF], vertical oscillation, leg stiffness) were recorded. Carbohydrate intake was standardized (90 g·h⁻¹). Repeated-measures ANOVA assessed changes over time.
RESULTS:
During the 180-min run, V̇O2, RER, blood lactate and energy cost remained stable, while heart rate and RPE increased (p<0.001). Carbohydrate oxidation decreased and fat oxidation increased (p<0.001). GCT and DF increased early and then stabilized (p<0.05), cadence and stride length remained stable, vertical oscillation decreased slightly, and leg stiffness was unchanged. Uphill time-trial performance declined (~7%, p<0.001), with shorter stride length and higher GCT and DF, while V̇O2 and energy cost were preserved.
CONCLUSION:
Trained trail runners preserved metabolic cost during prolonged subthreshold running despite rising cardiovascular and perceptual strain, indicating physiological durability. Concurrent small shifts toward a more terrestrial gait (higher GCT and DF) suggest adaptive mechanical reorganization that supports energetic stability rather than biomechanical deterioration. Performance decrements in uphill time trials reflect accumulated fatigue with preserved metabolic efficiency. Durability in trail running is multidimensional, integrating physiological resilience with compensatory biomechanical adaptations.