Introduction: The objective of this study was to determine whether the ratio of positive-to-negative mechanical work at the ankle, knee, and hip during level and inclined running is associated with running economy, quantified as the relative gross energy cost of transport (ECOT), in recreational runners. We hypothesized that runners with a higher positive-to-negative work ratio at the ankle and knee joints would demonstrate better ECOT 1,2, reflecting greater reliance on concentric work at these joints. Methods: Recreational runners (n= 26; 14 F; age: 33.7 ± 12.8 years;) completed 10-minute treadmill running trials at three grades (0%, 5% 2.9°, and 10% 5.7°) in a randomized order. The 0% trial was performed at 80% speed at lactate turn point, while the incline trials were run at slower speeds to maintain effort below lactate turn point. Marker position data were collected (fs=200 Hz) using an eight-camera motion capture system (Motion Analysis Corp, Rohnert Park, CA), synchronized with ground reaction forces (fs=1000 Hz) from a force instrumented treadmill (Bertec, Columbus, OH). Ankle plantar flexor, knee extensor, and hip flexor joint moments were calculated using an inverse dynamics model in Visual3D (C-Motion Inc., Germantown, MD). Joint-specific positive and negative mechanical work were calculated for the ankle, knee and hip during stance phase across all grades, and positive-to-negative work ratios were computed for each joint. Metabolic power (W) was calculated from VO 2 and VCO 2 using the Péronnet and Massicotte equation. ECOT (J/kg/km) was obtained by dividing metabolic power by running speed (m/s) and multiplying by 1000. Pearson correlations were performed in SPSS (IBM Corp., Armonk, NY) to examine relationships between ECOT and joint work ratios at each grade. Results: Across all joints and grades, correlations between ECOT and positive-to-negative work ratios were nonsignificant (p > 0.14). Representative values include ankle 10% (r=-0.29, p=0.146), hip 5% (r=0.29, p=0.150), and knee level ground (r=0.15, p=0.473). Joint work ratios were strongly correlated across grades within each joint (e.g., ankle 5% vs ankle 10% r= 0.76, p < 0.001). Individuals maintained nearly identical ankle, knee, and hip work ratios across all inclines. Conclusion: ECOT in recreational runners was not associated with the mechanical ratio of positive and negative work at any of these test joints or inclines. These findings suggest that inter-individual differences in ECOT are not determined by joint level work distribution. References: Cavagna G. A., et al., J Physiology, 268(2): 467-481, 1977. Van Hooren, B., et al., Sports Med, 54(5): 1269-1316, 2024. Funding: This work was supported by the Wu Tsai Human Performance Alliance and the Joe and Clara Tsai Foundation. Footwear was provided by Brooks Running. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.
Massarat et al. (Fri,) studied this question.