Single AFT Contributors To Running Economy Changes Are Detectable Independent Of Quantification Method

Advantages of using energy cost (EC) over oxygen cost (OC) to describe running economy (RE) include greater validity when substrate utilization is altered and greater sensitivity when interventions produce small differences. Single attributes of advanced footwear technology (AFT) that improve RE have not been systematically explained and any attribute is likely to contribute small effects. PURPOSE: The aim of this study was to compare the effects of single AFT shoe attributes on RE using both EC and OC quantification methods. METHODS: Experienced male runners (n = 12) completed 8 x 5-minute blocks of treadmill running at ~70% of estimated critical speed (RER = 0.87 ± 0.04) in four bespoke, mass adjusted AFT shoes. A prototype control (P) was compared to three other prototypes differing in resilience (R), compliance (C) or stack height (S; with additional small differences in geometry and plate). Shoes were tested in randomized, mirrored order with a 1:1 work-to-rest ratio. RE was measured by open circuit spirometry using 20-s averages of gross VO2 and VCO2 over the final 2-minutes of steady-state running in each block. The mass-specific EC (kcal/kg/km; Brockway) or OC (ml/kg/km) per unit distance were each used to compare within-condition AFT prototype pairings. RESULTS: Main effects of shoe type on RE were found (RM ANOVA) and Dunnett’s post-hoc test revealed that lower AFT shoe compliance (P vs C) significantly worsened RE when measured as EC (10/12; 1.57%; p = 0.009) and OC (10/12; 1.21%; p = 0.004). The effects of lower AFT resilience (P vs R) were consistent but smaller and nonsignificant in both EC (10/12; 0.72%; p = 0.277) and OC (9/12; 0.69%; p = 0.265). Stack height (P vs S) resulted in nonsignificant and less consistent effects on RE for both EC (7/12; 0.60%; p = 0.470) and OC (9/12; 0.59%; p = 0.416). There was no effect of AFT shoe attributes on RER (p = 0.296). CONCLUSIONS: Changes in single AFT attributes of resilience and compliance produced small (0.69 to 1.57%), but consistent directional changes in RE on the individual level (75 to 83% of pairs, i.e., 9/12 to 10/12). RE differences greater than ~1% were detected (p < 0.05) equally using EC and OC under conditions when RER did not differ.