Smartphone App (2kmFIT-App) for Measuring Cardiorespiratory Fitness: Validity and Reliability Study Muntaner Mas, Adrià Martínez Nicolás, Antonio Quesada, Alberto Cadenas Sánchez, Cristina Ortega Porcel, Francisco Bartolomé Exercise test Mobile apps Reproducibility of results Physical fitness Telemedicine Cardiorespiratory fitness FBO research activity was supported by the Spanish Ministry of Economy and Competitiveness—MINECO/FEDER DEP2016-79512-R; the European Union’s Horizon 2020 research and innovation program under Grant Agreement No. 667302; the University of Granada, Plan Propio de Investigación 2016, Unit of Excellence on Exercise and Health (UCEES); the Junta de Andalucía, Consejería de Conocimiento, Investigación y Universidades, and European Regional Development Fund (ERDF), ref. SOMM17/6107/ UGR; the EXERNET Research Network on Exercise and Health in Special Populations (DEP2005-00046/ACTI); and the SAMID III network, RETICS, funded by the PN I+D+I 2017-2021 (Spain), ISCIII Sub-Directorate-General for Research Assessment and Promotion, the European Regional Development Fund (ERDF) (Ref. RD16/002). AN was supported by the Ministry of Economy and Competitiveness and the Instituto de Salud Carlos III through the CIBERFES (CB16/10/00239), the Seneca Foundation through the unit of excellence (Grant 19899/GERM/15), and the Ministry of Science Innovation and Universities RTI2018-093528-B-I00 (all of which are cofinanced by FEDER). CCS is supported by the Spanish Ministry of Science, Innovation and Universities (FJC2018-037925-I). The views expressed are those of the authors and do not reflect the official policy or position of the institutions they belong to. Background: There is strong evidence suggesting that higher levels of cardiorespiratory fitness (CRF) are associated with a healthier metabolic profile, and that CRF can serve as a powerful predictor of morbidity and mortality. In this context, a smartphone app based on the 2-km walk test (UKK test) would provide the possibility to assess CRF remotely in individuals geographically distributed around a country or continent, and even between continents, with minimal equipment and low costs. Objective: The overall aim of this study was to evaluate the validity and reliability of 2kmFIT-App developed for Android and iOS mobile operating systems to estimate maximum oxygen consumption (VO2max) as an indicator of CRF. The specific aims of the study were to determine the validity of 2kmFIT-App to track distance and calculate heart rate (HR). Methods: Twenty participants were included for field-testing validation and reliability analysis. The participants completed the UKK test twice using 2kmFIT-App. Distance and HR were measured with the app as well as with accurate methods, and VO2max was estimated using the UKK test equation. Results: The validity results showed the following mean differences (app minus criterion): distance (& ndash;70.40, SD 51.47 meters), time (& ndash;0.59, SD 0.45 minutes), HR (& ndash;16.75, SD 9.96 beats/minute), and VO2max (3.59, SD 2.01 ml/kg/min). There was moderate validity found for HR (intraclass correlation coefficient [ICC] 0.731, 95% CI & ndash;0.211 to 0.942) and good validity found for VO2max (ICC 0.878, 95% CI & ndash;0.125 to 0.972). The reliability results showed the following mean differences (retest minus test): app distance (25.99, SD 43.21 meters), app time (& ndash;0.15, SD 0.94 seconds), pace (& ndash;0.18, SD 0.33 min/km), app HR (& ndash;4.5, 13.44 beats/minute), and app VO2max (0.92, SD 3.04 ml/kg/min). There was good reliability for app HR (ICC 0.897, 95% CI 0.742-0.959) and excellent validity for app VO2max (ICC 0.932, 95% CI 0.830-0.973). All of these findings were observed when using the app with an Android operating system, whereas validity was poor when the app was used with iOS. Conclusions: This study shows that 2kmFIT-App is a new, scientifically valid and reliable tool able to objectively and remotely estimate CRF, HR, and distance with an Android but not iOS mobile operating system. However, certain limitations such as the time required by 2kmFIT-App to calculate HR or the temperature environment should be considered when using the app. 2021-04-30T11:19:30Z 2021-04-30T11:19:30Z 2021-01-08 info:eu-repo/semantics/article Muntaner-Mas A, Martinez-Nicolas A, Quesada A, Cadenas-Sanchez C, Ortega FB Smartphone App (2kmFIT-App) for Measuring Cardiorespiratory Fitness: Validity and Reliability Study JMIR Mhealth Uhealth 2021;9(1):e14864. [https://doi.org/10.2196/14864] http://hdl.handle.net/10481/68247 10.2196/14864 eng info:eu-repo/grantAgreement/EC/H2020/667302 http://creativecommons.org/licenses/by/3.0/es/ info:eu-repo/semantics/openAccess Atribución 3.0 España JMIR Publications