A fixed, not proportional, cycling–treadmill heart rate bias at the ventilatory thresholds: a randomized crossover trial

Cycling elicits lower heart rates than treadmill exercise at equivalent metabolic intensities, but published estimates of this difference at ventilatory thresholds range widely (5–20 beats/min), preventing clinicians from reliably translating exercise prescriptions across modalities. This study aimed to determine whether the cycling–treadmill heart rate (HR) discrepancy at ventilatory thresholds is fixed or proportional, and to identify modality-independent intensity markers for rehabilitation exercise prescription. Twenty-three healthy adults completed a prospective, randomized, two-period crossover trial involving cardiopulmonary exercise testing (CPET) on a cycle ergometer and treadmill using the Porszász Unified Ramp Protocol, which mathematically equated metabolic work-rate progression across modalities. Bland–Altman regression characterized bias structure at the first (VT1) and second (VT2) ventilatory thresholds. Cycling HR was significantly lower at VT1 (118.9 ± 7.4 vs. 132.4 ± 7.7 beats/min; difference − 13.5 beats/min; 95% CI − 14.5 to − 12.6; P < 0.001) and VT2 (154.5 ± 13.6 vs. 169.3 ± 13.4 beats/min; difference − 14.8 beats/min; 95% CI − 19.4 to − 10.2; P < 0.001). Regression slopes were non-significant at both thresholds (VT1: β=−0.047, P = 0.459; VT2: β=+0.019, P = 0.919), confirming fixed bias. VE/VCO₂ showed no significant modality difference at either threshold (both P > 0.80). The cycling–treadmill HR discrepancy constitutes a fixed bias of approximately 14 beats/min in healthy adults, statistically justifying a universal correction factor; individual-modality calibration CPET is not required. This fixed offset is proportionally larger at lower HRmax and should not be applied uncritically in older or at-risk populations. VE/VCO₂ provides a correction-free, modality-independent intensity anchor that does not require age- or population-specific recalibration . Replication in clinical rehabilitation populations is warranted before adoption in patients with cardiovascular or pulmonary disease. ClinicalTrials.gov NCT07718594. Registered 14 July 2026. Retrospectively registered.