Estimating V̇O₂ max in healthy subjects without maximal effort: a novel protocol using ballistocardiography

Low maximal oxygen uptake (V̇O₂ max) is a strong predictor of cardiovascular morbidity and mortality, yet its gold-standard assessment through cardiopulmonary exercise testing (CPET) requires maximal effort and specialized equipment. This study evaluates whether ballistocardiography (BCG), recorded during brief stabilization breaks embedded in a submaximal cycling protocol, can provide reliable estimates of V̇O₂ max. BCG provides unique insights into stroke volume and blood displacement, offering a robust physiological basis for V̇O₂ max estimation. Sixteen healthy young adults completed three randomized exercise protocols on a cycle ergometer with simultaneous gas-exchange analysis: a standard incremental step CPET until exhaustion (S) and two modified protocols including short breaks (B1 and B2) designed to facilitate high-quality BCG acquisition. BCG-derived kinetic output (KVO₂) was used to predict V̇O₂ max through a linear regression model based on early-stage workload increments. Both break-based protocols yielded CPET-measured V̇O₂ max and maximal workload values comparable to those from the standard test. BCG-based V̇O₂ max estimation, using only the first breaks of the protocol, which require a total exercise duration of 10.1 (9.5; 10.8) minutes without reaching maximal effort, demonstrated accuracy comparable to maximal standard tests, with a coefficient of variation of 12.05% and a mean absolute percentage error of 15.59%. While this study was limited to healthy young adults, the proposed approach holds potential for broader applications, particularly in diverse settings or in populations where maximal effort is impractical. Future work should focus on integrating additional BCG signal features and validating these methods in diverse populations.