Quantifying Running Economy in Amateur Runners: Evaluating VO₂ and Energy Cost with Model-based Normalization

Submaximal oxygen uptake (VO_2sub) scaled by ratio is commonly used to evaluate running economy (RE) to reflect metabolic consumption at a given submaximal-intensity velocity. However, this method is questionable due to its neglect of substrate-related issues and the inherent mathematical discrepancies in ratio scaling. This study aimed to investigate the validity of ratio-scaled VO_2sub as a measure of RE by comparing it with allometric-scaled energy cost (E_c, kcal/kg^b/min). Sixty-nine recreationally active college students underwent VO_2max tests and discontinuous submaximal running assessments at three %VO_2max intensities. A 1000-meter test assessed running performance. One-way repeated-measures ANOVA compared changes in VO_2sub or E_c with increasing running intensities. Regression analysis explored methods for metabolic data standardization. Pearson correlation coefficient evaluated the effectiveness of standardization and the correlations between sports performance and RE scaled by different measures. Magnitude-based inferences were used to assess sex differences and probabilities of RE at each running intensity. Both VO_2sub and E_c significantly increased with increasing intensities, suggesting that VO_2sub is a valid quantification of RE. Allometric scaling is more suitable than ratio scaling for removing the influence of body weight on both E_c and VO_2sub, with females showing better RE. Allometric-scaled E_c was sensitive in detecting correlations with performance, strongest at 65% VO_2max. While VO_2sub is a valid quantification of RE, allometric scaling, rather than ratio scaling, should be used to normalize the RE quantification before performing reliable interindividual comparisons. The 2/3 law can be considered as the exponent b value for body weight. Additionally, 65%VO_2max intensity is recommended as the submaximal testing intensity in the RE test. Nonetheless, more studies with diverse samples are needed to confirm the validity.