Greater Ankle Plantar Flexor Work Is Predictive of Better Running Economy on Steep Uphill Grades

The purpose of this study was to determine the influence of lower extremity joint kinetics and muscle strength on running economy (RE) over level ground, 5% and 10% grades. Twenty-seven recreational runners (14 females, age: 33.7 [12.8] y, mass: 70.2 [12.5] kg, height: 175.9 [9.1] cm) completed laboratory-based RE, biomechanics, and isokinetic dynamometry testing. Linear regression analyses were used to determine the effect of lower extremity joint work, stiffness, and strength on RE for each grade. Greater ankle plantar flexor work was predictive of better economy when running on the 10% grade (β = -3054.56; P = .013), but not the level ground or 5% grade (P > .05). No other joint work, stiffness, or strength factors were related to RE. A secondary analysis explored the relationship of training factors to RE, demonstrating better 10% grade RE (P = .015) and greater ankle work (P = .048) in trail runners compared with road runners. The results of this study suggest that targeting the energy generation capacity of the plantar flexors may be worthwhile for improving uphill RE. Trail running may lead to specific physiological and biomechanical adaptations that are beneficial to performance.