Energy Cost of Running in Well-Trained Athletes: Toward Slope-Dependent Factors

Purpose: This study aimed to determine the contribution of metabolic, cardiopulmonary, neuromuscular, and biomechanical factors to the energy cost (ECR) of graded running in well-trained runners. Methods: Eight men who were well-trained trail runners (age: 29 [10] y, mean [SD]; maximum oxygen consumption: 68.0 [6.4] mL.min(-1).kg(-1)) completed maximal isometric evaluations of lower limb extensor muscles and 3 randomized trials on a treadmill to determine their metabolic and cardiovascular responses and running gait kinematics during downhill (DR: -15% slope), level (0%), and uphill running (UR: 15%) performed at similar O-2 uptake (approximately 60% maximum oxygen consumption). Results: Despite similar O-2 demand, ECR was lower in DR versus level running versus UR (2.5 [0.2] vs 3.6 [0.2] vs 7.9 [0.5] J.kg(-1).m(-1), respectively; all P < .001). Energy cost of running was correlated between DR and level running conditions only (r(2) = .63; P = .018). Importantly, while ECR was correlated with heart rate, cardiac output, and arteriovenous O-2 difference in UR (all r(2) > .50; P < .05), ECR was correlated with lower limb vertical stiffness, ground contact time, stride length, and step frequency in DR (all r(2) > .58; P < .05). Lower limb isometric extension torques were not related to ECR whatever the slope. Conclusion: The determining physiological factors of ECR might be slope specific, mainly metabolic and cardiovascular in UR versus mainly neuromuscular and mechanical in DR. This possible slope specificity of ECR during incline running opens the way for the implementation of differentiated physiological evaluations and training strategies to optimize performance in well-trained trail runners.

Automated summary

This study aimed to determine the factors contributing to energy cost during graded running in well-trained runners. The results showed that energy cost was lower during downhill running compared to level and uphill running, and the correlations between energy cost and physiological factors differed depending on the slope.