# Body composition, maximal fitness, and submaximal exercise function in people with interstitial lung disease

## TL;DR

The study explores how body composition and exercise capacity relate in people with lung disease, suggesting fat-free mass is a better measure than body weight and identifying a potential submaximal exercise marker.

## Contribution

The study introduces fat-free mass as a better scaling factor for exercise capacity and identifies OUEP as a promising submaximal marker in interstitial lung disease.

## Key findings

- VO2peak scaled to fat-free mass shows women have higher values than men in interstitial lung disease patients.
- OUEP is significantly correlated with lung function and moderately agrees with VO2peak.
- Ratio-standard scaling is sufficient for adjusting VO2peak for body size effects.

## Abstract

Cardiopulmonary exercise testing (CPET) is feasible, valid, reliable, and clinically useful in interstitial lung disease (ILD). However, maximal CPET values are often presented relative to body mass, whereas fat-free mass (FFM) may better reflect metabolically active muscle during exercise. Moreover, despite the value of maximal parameters, people with ILD do not always exercise maximally and therefore clinically relevant submaximal parameters must be identified. Therefore, this study assessed peak oxygen uptake (VO2peak) relative to FFM, identifying the validity of common scaling techniques; as well as characterising the oxygen uptake efficiency slope (OUES) and plateau (OUEP) as possible submaximal parameters.

Participants with ILD underwent assessment of body composition and CPET via cycle ergometry during a single study visit. To determined effectiveness of scaling for body size, both body mass and FFM were scaled using ratio-standard (X/Y) and allometric (X/Yb) techniques. Pearsons’s correlations determined agreement between OUES, OUEP, and parameters of lung function. Cohens kappa (κ) assessed agreement between OUES, OUEP and VO2peak.

A total of 24 participants (7 female; 69.8 ± 7.5 years; 17 with idiopathic pulmonary fibrosis) with ILD completed the study. Maximal exercise parameters did not require allometric scaling, and when scaled to FFM, it was shown that women have a significantly higher VO2peak than men (p = 0.044). Results also indicated that OUEP was significantly and positively correlated with DLCO (r = 0.719, p < 0.001), and held moderate agreement with VO2peak (κ = 0.50, p < 0.01).

This study identified that ratio-standard scaling is sufficient in removing residual effects of body size from VO2peak, and that VO2peak is higher in women when FFM is considered. Encouragingly, this study also identified OUEP as a possible alternative submaximal marker in people with ILD, and thus warrants further examination.

The online version contains supplementary material available at 10.1186/s12931-025-03195-9.