Oxygen cost (OC) is commonly employed to assess an athlete's running economy, though the validity of this measure is often overlooked.
Purpose: This study evaluated the validity of OC as a measure of running economy by comparison to the underlying energy cost (EC). Additionally, the most appropriate method of removing the influence of body mass was determined to elucidate a measure of running economy that enables valid inter-individual comparisons.
Methods: 172 highly trained endurance runners (males, n = 101; females, n = 71) performed a discontinuous submaximal running assessment, consisting of approximately seven 3 min stages (1 km [BULLET OPERATOR] hr-1 increments), to determine the absolute OC (L [BULLET OPERATOR] km-1) and EC (Kcal [BULLET OPERATOR] km-1) for the 4 speeds below lactate turnpoint.
Results: Comparisons between models revealed linear ratio scaling to be a more suitable method than power function scaling for removing the influence of body mass for both EC (R2; males, 0.589 vs 0.588; females, 0.498 vs 0.482) and OC (males, 0.657 vs 0.652; females, 0.532 vs 0.531). There were stepwise increases in EC and RER with increments in running speed (both, P < 0.001). However, no differences were observed for OC across the 4 monitored speeds (P = 0.54).
Conclusion: Whilst EC increased with running speed, OC was insensitive to changes in running speed, and therefore does not appear to provide a valid index of the underlying EC of running, likely due to the inability of OC to account for variations in substrate utilisation. Therefore, EC should be employed as the primary measure of running economy, and for runners an appropriate scaling with body mass-1 is recommended.
(C) 2014 American College of Sports Medicine