Relationship between advanced footwear technology longitudinal bending stiffness and energy cost of running

Introduction/Purpose Shoe longitudinal bending stiffness (LBS) is often considered to influence running economy (RE) and thus, running performance. However, previous results are mixed and LBS levels have not been studied in advanced footwear technology (AFT). The purpose of this study was to evaluate the isolated effects of increased LBS from curved carbon fiber plates embedded within an AFT midsole on RE and spatiotemporal parameters. Methods Twenty-one male trained runners completed 3 times 4 minutes at 13km/h with two experimental shoe models with a curved carbon fiber plate embedded in an AFT midsole with different LBS values (Stiff: 35.5 N/mm and Stiffest: 43.1 N/mm), and a Control condition (no carbon fiber plate: 20.1 N/mm). We measured energy cost of running (W/kg) and spatiotemporal parameters in one visit. Results RE improved for the Stiff shoe condition (15.71 ± 0.95 W/kg; p<0.001; n 2 =0.374) compared to the Control condition (16.13 ± 1.08 W/kg) and Stiffest condition (16.03 ± 1.19 W/kg). However, we found no significant differences between the Stiffest and Control conditions. Moreover, there were no spatiotemporal differences between shoe conditions. Conclusion Changes in LBS in AFT influences RE suggesting that moderately stiff shoes are the most effective LBS to improve RE in AFT compared to very stiff shoes and traditional, flexible shoe conditions while running at 13 km/h. ### Competing Interest Statement VRC has received a research grant from On Running, for a different study, FGM and JMGR have no conflicts of interest relevant to the content of this article. WH has received research grants from PUMA and Saucony. No footwear company had any influence on the conceptualization or presented in this publication. The results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation.