Validation of a Novel Incremental Step Test for Assessment of Cardiopulmonary Fitness and Ventilatory Thresholds in Adults

The purpose of this single-group diagnostic validation and test-retest reliability study is to determine whether a novel Incremental Step Test (IST) can accurately assess cardiorespiratory fitness and ventilatory thresholds in healthy adults compared with an established laboratory-based cycle ergometer Cardiopulmonary Exercise Test (CPET). The main questions are whether the step test can elicit reliable physiological responses sufficient to identify the anaerobic threshold and respiratory compensation point, and whether it produces reproducible results when repeated under standardised conditions. The study will compare the incremental step test (IST) with CPET to assess whether the IST provides similar peak and submaximal physiological measures and agreement with CPET comparator. Participants will complete three laboratory exercise tests across separate visits: one maximal CPET on a cycle ergometer, followed by two repeated ISTs performed on a 25 cm step board following the audio metronome.