Validity of the International Fitness Scale (IFIS) and its associations with cardiometabolic health and body composition in adults with type 2 diabetes: A cross-sectional study

Sep 29, 2026

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This cross-sectional study evaluated the validity of the International Fitness Scale (IFIS) for assessing cardiorespiratory fitness against the 6-minute walk test (6MWT) and examined construct validity for cardiometabolic and body composition outcomes. Among 282 adults with type 2 diabetes, self-reported IFIS domains (overall, cardiorespiratory, muscular, speed-agility, flexibility) were compared with objective 6MWT measures. Associations were tested using ANCOVA adjusted for sex and age, with ROC analyses using DeLong tests. IFIS showed graded relationships with 6MWT and meaningful links with cardiovascular health, MASLD, hs-CRP, BMI, visceral adipose tissue, and thigh fat-free muscle volume.

LanguageEnglish

CategoryResearch & Report

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Pages19

Reading Time48 min

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Abstract

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OPEN ACCESS Citation: Herraiz-Adillo Á, Rådholm K, Iredahl F, Carlhäll C-J, Roemkens N, Forsgren M, et al. (2026) Validity of the International Fitness Scale (IFIS) and its associations with cardiometabolic health and body composition in adults with type 2 diabetes: A cross-sectional study. PLoS One 21(1): e0339364. [https://doi](https://doi). org/10.1371/journal.pone.0339364 Editor: Georgian Badicu, Universitatea Transilvania din Brasov, ROMANIA Received: May 9, 2025 Accepted: December 7, 2025 Published: January 6, 2026 Peer Review History: PLOS recognizes the benefits of transparency in the peer review process; therefore, we enable the publication of all of the content of peer review and author responses alongside final, published articles. The editorial history of this article is available here: [https://doi.org/10.1371/journal](https://doi.org/10.1371/journal). pone.0339364 Copyright: © 2026 Herraiz-Adillo et al. This isan open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, RESEARCH ARTICLE Validity of the International Fitness Scale (IFIS) and its associations with cardiometabolic health and body composition in adults with type 2 diabetes: A cross-sectional study Ángel Herraiz-Adillo1, Karin Rådholm2,3, Fredrik Iredahl4,5, Carl-Johan Carlhäll1,6, Nahuel Roemkens1, Mikael Forsgren1,6,7, Olof Dahlqvist Leinhard1,6,8, Peter Lundberg1,6,8,9, Stergios Kechagias1, Nils Dahlström1,6,8, Patrik Nasr1,5,6, Mattias Ekstedt1,6*☯, Pontus Henriksson1*☯ 1 Department of Health, Medicine and Caring Sciences, Linköping University, Linköping, Sweden, 2 Primary Health Care Center Kärna, and Department of Health, Medicine and Caring Sciences, Linköping University, Linköping, Sweden, 3 The George Institute for Global Health, University of New South Wales, Sydney, Australia, 4 Primary Health Care Center Åby, and Department of Health, Medicine and Caring Sciences, Linköping University, Linköping, Sweden, 5 Wallenberg Center for Molecular Medicine (WCMM), Linköping University, Linköping, Sweden, 6 Center for Medical Image Science and Visualization (CMIV), Linköping University, Linköping, Sweden, 7 AMRA Medical AB, Linköping, Sweden, 8 Clinical Department of Radiology in Linköping, Region Östergötland, Linköping, Sweden, 9 Clinical Department of Medical Radiation Physics, Region Östergötland, Linköping, Sweden ☯ These authors contributed equally to this work and are shared senior authors on this work. * [pontus.henriksson@liu.se](pontus.henriksson@liu.se) (PH); [mattias.ekstedt@liu.se](mattias.ekstedt@liu.se) (ME) Abstract Aims To assess the validity of the International Fitness Scale (IFIS) for evaluating cardiorespiratory fitness compared to the 6-minute walk test (6MWT) (criterion validity) and to examine associations with cardiometabolic and body composition outcomes (construct validity) . Methods A cross-sectional analysis was conducted on 282 adults with type 2 diabetes mellitus (T2DM) (mean age 63.6 ± 8.1 years, 37.9% women) . Self-reported fitness was assessed using IFIS, including overall, cardiorespiratory, muscular, speed-agility and flexibility scores. Objective cardiorespiratory fitness was assessed using the 6MWT. Associations with 6MWT, cardiometabolic (i.e. , cardiovascular health score, metabolic dysfunction-associated steatotic liver disease [MASLD], high-sensitivity C-reactive protein) and body composition outcomes (i.e. , body mass index [BMI], visceral adipose tissue volume, thigh fat-free muscle volume) were analyzed using ANCOVA (adjusted by sex and age) and ROC curves, compared using DeLong tests. PLOS One | [https://doi.org/10.1371/journal.pone.0339364](https://doi.org/10.1371/journal.pone.0339364) January 6, 2026 1 / 19 distribution, and reproduction in any medium, provided the original author and source are credited. Data availability statement: The data underlying this article cannot be made publicly

FAQs

What was the study’s main purpose for evaluating the IFIS?

To assess IFIS validity for cardiorespiratory fitness compared with the 6MWT (criterion validity) and to examine relationships with cardiometabolic and body composition outcomes (construct validity).

How were fitness and health outcomes measured in the study?

Fitness was self-reported using IFIS (overall and multiple domains) and assessed objectively with the 6-minute walk test (6MWT). Cardiometabolic outcomes included cardiovascular health score, MASLD, and hs-CRP, while body composition included BMI, visceral adipose tissue volume, and thigh fat-free muscle volume.

What statistical approaches were used to test validity and associations?

ANCOVA adjusted for sex and age evaluated associations with outcomes, and ROC curve analyses assessed discriminatory performance, with DeLong tests used for comparisons.

Sep 29, 2026

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