The Valid Measurement of Running Economy in Runners

Oxygen cost (O-C) is commonly used to assess an athlete's running economy, although the validity of this measure is often overlooked. Purpose: This study evaluated the validity of O-C as a measure of running economy by comparison with the underlying energy cost (E-C). In addition, the most appropriate method of removing the influence of body mass was determined to elucidate a measure of running economy that enables valid interindividual comparisons. Methods: One hundred and seventy-two 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.h(-1) increments), to determine the absolute O-C (L.km(-1)) and E-C (kcal.km(-1)) for the four speeds below lactate turn point. 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 E-C (males, R-2 = 0.589 vs 0.588; females, R-2 = 0.498 vs 0.482) and O-C (males, R2 = 0.657 vs 0.652; females, R2 = 0.532 vs 0.531). There were stepwise increases in E-C and RER with increments 0.482) and O-C (males, R-2 = 0.657 vs 0.652; females, R-2 = 0.532 vs 0.531). There were stepwise increases in E-C and RER with increments in running speed (both, P < 0.001). However, no differences were observed for O-C across the four monitored speeds (P = 0.54). Conclusions: Although E-C increased with running speed, O-C was insensitive to changes in running speed and, therefore, does not appear to provide a valid index of the underlying E-C of running, likely due to the inability of O-C to account for variations in substrate use. Therefore, E-C should be used as the primary measure of running economy, and for runners, an appropriate scaling with body mass(-1) is recommended.