Substrate-Corrected VO₂ Models for Improved Interpretation of Movement Economy Technical Report

Abstract

Introduction: Movement economy is a core metric in endurance performance, yet conventional interpretation overlooks substrate-specific oxygen costs. Elevated oxygen consumption (VO₂) is often misclassified as reduced efficiency when it may instead reflect adaptive increases in fat oxidation. This report introduces and evaluates normalization approaches designed to yield more physiologically valid interpretations of oxygen consumption.

Methods: This conceptual, simulation-based, and secondary data analysis developed two substrate-corrected VO₂ models: (1) the RER-Based Energy Equivalent (RER-EE) model, which adjusts VO₂ for varying caloric yields per liter of oxygen across RER values, and (2) the RER-Based Substrate Partitioning with Substrate Correction Ratio (RER-SP+SCR) model, which partitions VO₂ by substrate and corrects the fat-derived fraction for its lower ATP yield per O₂. Both were applied to previously published datasets from endurance athletes under diverse metabolic conditions.

Results: Both models produced appreciably different normalized VO₂ values compared to traditional methods, particularly under high-fat oxidation conditions. The largest corrections occurred during prolonged submaximal efforts, such as 13KM and 25KM trials, reducing bias that would otherwise misclassify fat-adapted athletes as less economical.

Conclusions: Substrate-corrected normalization provides a physiologically valid framework for interpreting oxygen consumption, enhancing research and applied assessments of endurance performance, training adaptation, and metabolic health.