Influence of midsole ‘actuator lugs’ on running economy in trained distance runners

Introduction: Previous investigations reported the influence of running shoe design on running economy (RE) and determined that both shoe weight and midsole properties (hardness, stiffness, comfort) can alter RE. External forefoot actuator lugs have been reported to provide enhanced energy return during shoe mechanical testing, but it was unclear if this design feature would provide any improvement of RE. The current investigation measured the effects of external forefoot actuator lugs on RE in 12 highly-trained male distance runners during four submaximal running velocities. Methods: All runners voluntarily completed a maximal graded exercise treadmill protocol followed 5–7 days later by eight randomised 6 min submaximal level-grade treadmill runs with two randomised footwear conditions (WL = with lugs, WOL = without lugs). Oxygen consumption, heart rate (HR), rating of perceived effort (RPE), and sagittal plane high-speed video were collected. RE (metres run per millilitre O2 per kg of body mass), stance duration (ST), stride rate (SR), and foot strike (FS) were computed for each trial. Data were analysed with factorial repeated-measures analysis of variance (ANOVA). Results: RE, averaged over all submaximal velocities, was significantly greater (p < 0.05) in the WL condition (4.96 ± 0.12 m·ml−1·kg−1) as compared to the WOL condition (4.91 ± 0.10 m·ml−1·kg−1). Only one subject displayed a lower RE in the WL condition. No significant differences were found between HR (p > 0.05), ST (p > 0.05), or SR (p > 0.05) between footwear conditions, but running in the WL condition lowered RPE (p < 0.05). Conclusions: The presence of external forefoot actuator lugs improved RE by ∼1%, although the mechanisms explaining this improvement are not clear.