# An evidence-based multi-factorial model to predict the oxygen cost of ventilation during ramp-incremental cycle ergometry exercise

## TL;DR

This study creates a model to estimate the oxygen cost of breathing during intense cycling exercise and shows it significantly affects oxygen uptake measurements.

## Contribution

A novel non-linear model predicts oxygen cost of ventilation and its impact on maximal oxygen uptake estimates during ramp-incremental cycling.

## Key findings

- The model explains 81% of variance in oxygen cost of ventilation (V̇O2VENT).
- V̇O2VENT contributes 17.43% of total oxygen uptake at maximal exercise.
- Correcting for V̇O2VENT significantly lowers estimated oxygen uptake values near exhaustion.

## Abstract

During maximal ramp-incremental exercise (RIE), the oxygen uptake–power output relationship (
V˙
O2gain) may deviate from linearity near exhaustion. An increased oxygen cost of ventilation (
V˙
O2VENT) is a plausible but under-quantified contributor. This study tested a non-linear multi-factorial model using measured
V˙
O2VENT and six predictors: resting expired ventilation (
V˙

E), weight, height, age,
V˙
O2 peak, and maximal heart rate (HRMax) to 1) estimate
V˙
O2VENT and its contribution to maximal oxygen uptake (
V˙
O2max) in an independent dataset and 2) determine whether correcting
V˙
O2 by
V˙
O2VENT (
V˙
O2VCORR) alters
V˙
O2max and
V˙
O2gain estimates.

Published data from 42 participants (11 women, 31 men; 29 ± 6.5 years;
V˙
O2max = 4.02 ± 1.06 L min−1) were used to derive the model. Leave-one-out cross-validation (LOOCV) was used to assess validity, with predictive accuracy and coefficient stability evaluated via bootstrap resampling. The model was applied to an independent RIE dataset to generate
V˙
O2VCORR, which was compared with uncorrected
V˙
O2 across six %Wpeak intensities using repeated-measures ANOVA and final 30 s slope analysis.

The model explained 81% of
V˙
O2VENT variance (adjusted R
2 = 0.78).
V˙
O2VENT represented 17.43% ± 3.58% of
V˙
O2 at
V˙
O2max. Across 35%–100% Wpeak,
V˙
O2VCORR values (L·min−1) increased with intensity (1.77 ± 0.43, 2.68 ± 0.57, 3.43 ± 0.72, 3.72 ± 0.79, 3.84 ± 0.86, and 3.92 ± 0.82) but remained significantly lower than uncorrected
V˙
O2 (p < 0.001), with the final-30 s
V˙
O2 slope attenuated following correction (p = 0.002).

The internally validated model revealed
V˙
O2VENT may contribute to a significant fraction of
V˙
O2 near exhaustion.