Calculation of a Conversion Factor to Estimate Anaerobic Energy in Trained Men and Women Runners

Authors

Austin B. Shaw, University of North Texas, DentonFollow
Ethan J. Hein, University of North Texas, DentonFollow
Brady C. McLain, University of North Texas, DentonFollow
Jacob L. McNary, University of North Texas, DentonFollow
Sarah E. Deemer, University of North Texas, DentonFollow
Lydia K. Caldwell, University of Dayton, DaytonFollow
David W. Hill, University of North Texas, DentonFollow

Abstract

Accurate quantification of anaerobic energy contribution is crucial for sport performance and bioenergetics research. A recently popularized method estimates anaerobic contribution and capacity from a single exercise test by multiplying post-exercise blood lactate by an oxygen equivalent (O₂–Eq–Lac; historically 2.7–3.3 mL·kg^–1·mM^–1). Foundational studies have empirically derived this conversion factor across modalities: two have reported 3.0–3.3 mL·kg^–1·mM^–1 for running, two have obtained 2.7 mL·kg^–1·mM^–1 for swimming, and one has determined 3.0 mL·kg^–1·mM^–1 for cycling. These studies are based on physiological assumptions (e.g., the caloric equivalent of lactate and the distribution of lactate in the body). A recent study, which did not rely on any of these assumptions, calculated a value of 3.4 ± 0.4 mL·kg^–1·mM^–1 for cycling exercise. None of these studies explored sex differences in the conversion factor. PURPOSE: To determine the O₂–Eq–Lac in trained women and men runners. METHODS: Twenty-five trained runners (13 men: age 29 ± 7 y, VO_2max 60 ± 6 mL·kg^–1·min^–1; 12 women: age 32 ± 7 y, VO_2max 49 ± 4 mL·kg^–1·min^–1) performed an incremental test to determine VO_2max and the second ventilatory threshold (VT2). The severe intensity speed was the velocity eliciting VO₂ = VT2 + 10% of Δ(VO_2max – VT2) (13 ± 2 km·hr^–1). Participants completed two 6-min constant-speed tests, in randomized order; one in normoxia (F_IO₂ = 21%) and one in hypoxia (F_IO₂ = 15%) with continuous measurement of VO₂ and minute ventilation. Blood lactate was assessed by fingerstick 4, 5, and 6 min post-exercise. Phosphocreatine (PCr) contribution was derived from recovery VO₂ kinetics. The increase in glycolytic contribution (mL·kg^–1) in hypoxia was assumed to equal the decrease in the aerobic contribution (accumulated VO₂, mL·kg^–1), corrected for the increase in the oxygen cost (mL·kg^–1) associated with the greater ventilation in hypoxia and the difference in PCr contribution (mL·kg^–1). The O₂–Eq–Lac was calculated as the ratio between the increase in glycolytic contribution divided by the increase in peak post-exercise blood lactate concentration (mM). RESULTS: Hypoxia reduced accumulated VO₂ (247 ± 42 vs. 228 ± 39 mL·kg^–1, p < 0.01) and increased peak blood lactate (5.0 ± 2.1 vs. 9.5 ± 3.7 mM, p < 0.01), accumulated ventilation (443 ± 126 vs. 511 ± 137 L, p < 0.01), and PCr (36 ± 4 vs. 42 ± 8 mL·kg^–1, p < 0.01). Overall, the O₂–Eq–Lac was 3.4 ± 0.4 mL·kg^–1·mM^–1. Men exhibited a lower O₂–Eq–Lac (3.2 ± 0.4 mL·kg^–1·mM^–1) than women (3.6 ± 0.3 mL·kg^–1·mM^–1, p < 0.01, d = 1.81). CONCLUSION: The novel finding in this study is that sex differences in the O₂–Eq–Lac were observed. We speculate that the difference may be related to muscle fiber type composition or lactate clearance. The implication is that sex-specific values should be recommended for accurate estimation of anaerobic capacity in runners.

Recommended Citation

Shaw, Austin B.; Hein, Ethan J.; McLain, Brady C.; McNary, Jacob L.; Deemer, Sarah E.; Caldwell, Lydia K.; and Hill, David W. (2026) "Calculation of a Conversion Factor to Estimate Anaerobic Energy in Trained Men and Women Runners," International Journal of Exercise Science: Conference Proceedings: Vol. 2: Iss. 18, Article 81.
Available at: https://digitalcommons.wku.edu/ijesab/vol2/iss18/81