Introduction: The reasons underlying the considerable interindividual differences in running economy (RE) changes in shoes with advanced footwear technology (AFT) (Hoogkamer et al., Citation2018) are still largely unknown. Furthermore, the result improvements in distance running in the years since AFT was introduced have been greater for elite females compared to males (Bermon et al., Citation2021; Mason et al., Citation2024). A number of characteristics may be relevant for these differences and lower extremity muscle strength may be a contributing factor. Purpose of the study: The aim of this study was to investigate the relationship of open-chain muscle strength in various isolated lower extremity muscles and closed-chain leg strength in a leg-press with differences between AFT shoes with high energy return (ER) and a non-AFT shoe with lower ER. This aim was designed to illuminate strength as a possible factor for explaining discrepancies between females and males in the performance enhancing benefits provided by AFT shoes. Methods: Isokinetic open- and closed-chain strength was assessed in an isokinetic dynamometer (Isomed2000, DRFerstl GmbH, Henau, Germany) in 30 high-level runners (15 female, 15 male) when running at 60, 70 and 80% of their VO2max velocity on a treadmill in an advanced footwear technology (AFT) shoe and a control, non-AFT shoe. The strength was measured in the triceps surae, tibialis anterior, quadriceps and hamstring muscles and in a closed-chain leg-press. The difference in running economy (RE) between the shoe conditions was correlated with the muscle strengths. Results: No significant correlations were seen between RE improvements in the AFT shoe compared to the control shoe in open-chain isokinetic strength in isolated muscle groups, however this improved RE correlated significantly with strength in the closed chain leg-press at 70% of VO2max speed for males and at 60 and 80% for females. Interestingly, the correlation was negative for males and positive for females. For females a stronger leg-press correlated significantly with an improved RE in the AFT shoe at two of the three running speeds.
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