Durability in Trail Running: Coupled Physiological and Biomechanical Responses to Prolonged Submaximal and Repeated Uphill Time Trials in Trained Trail Runners

Purpose : This study examined the durability of physiological and biomechanical responses in trained trail runners during prolonged submaximal running combined with repeated uphill efforts. Methods : Twenty-three trail runners (11 females) completed a 180-minute treadmill run at 85% of the speed associated with their lactate threshold +0.5 mmol·L −1 (ie, steady state). Every 60 minutes, participants performed a 12-minute uphill time trial (+12%). Physiological variables (oxygen uptake [ ], respiratory exchange ratio [RER], blood lactate [BLa], substrate oxidation, heart rate, and perceived exertion) and gait parameters (stride length, cadence, ground contact time, duty factor, vertical oscillation, and leg stiffness) were continuously recorded. Results : By the end of steady-state running, heart rate and perceived exertion increased ( P  < .001), whereas , BLa, and energy cost remained stable. Carbohydrate oxidation decreased ( P  < .001), while fat oxidation increased ( P  < .001). Across uphill time trials, distance (−6.6%, P  < .001) and stride length declined, while ground contact time and duty factor increased; RER and BLa decreased (both P  < .001), indicating a progressive metabolic shift toward greater fat reliance. Despite these changes, oxygen cost and leg stiffness were preserved. Conclusions : Prolonged submaximal and repeated uphill running induced small but coordinated physiological and mechanical drifts without compromising overall energetic cost. These findings reveal high durability in trained trail runners, reflected in their ability to preserve biomechanical stability and running efficiency despite increasing perceived fatigue.