The Ability of Stryd Footpod Metrics to Reflect Changes in Metabolic Power Between Running Shoe Types

It is unclear if running power (RP) estimated by the Stryd footpod device maintains its linear relationship to metabolic power (W_MET) when switching between training and racing shoe types. This study determined if RP estimated by the Stryd footpod and its other spatiotemporal metrics reflect the improvement (decrease) in W_MET when wearing high-performance racing shoes (HPRS; Nike AlphaFly Next%) compared to control training shoes (CTS; Nike Revolution 5). Fourteen well-trained runners completed two treadmill tests: Absolute Velocity Running Test (AVRT; 11.3-14.5 km·hr^-1) and Relative Velocity Running Test (RVRT; 55-75% VO_2MAX). W_MET was determined with indirect calorimetry. RP was not significantly different between shoe types (p > 0.432) during the AVRT, but W_MET was ~5% lower in HPRS (p < 0.001). During the RVRT, participants ran ~6% faster and at ~6% higher RP (both, p < 0.001) in HPRS for the same W_MET (p = 0.869). Linear mixed models confirmed W_MET was ~5% lower in HPRS for a given RP (p < 0.001). Still, RP and W_MET were strongly related within shoe types (p < 0.001, conditional-R² = 0.982, SEE = 2.57%). Form power ratio and ground contact time correlated with energetic cost (p < 0.011) but did not fully reflect the influence of shoe type. Therefore, runners should account for their shoe type when using RP to indicate W_MET between training and racing.