Evaluation of Heart Rate and Ventilatory Threshold Agreement Between Cycling and Running Under Strictly Standardized Ramp Conditions

Participants Twenty-three healthy adults (12 men, 11 women; age 30.8 ± 5.6 years; BMI 21.8 ± 2.6 kg/m²) were recruited via institutional advertisements at a university hospital. Inclusion criteria were: age ≥ 20 years, familiarity with cycling and treadmill exercise, and a negative Physical Activity Readiness Questionnaire response. Exclusion criteria were: history of cardiovascular, pulmonary, or metabolic disease; musculoskeletal injuries limiting exercise range of motion; or medications affecting heart rate or ventilation. Participants fasted for 3 hours, abstained from vigorous exercise, alcohol, and caffeine for 24 hours prior to testing, and provided written informed consent. Data collection was conducted between February 2024 and November 2024. The protocol was approved by the Institutional Review Board of National Taiwan University Hospital (IRB Registration: 202311036RIND).

Experimental Design A randomized crossover design was employed. Participants completed two symptom-limited CPET sessions on a cycle ergometer (VIAsprint, Ergoline, Germany) and motorized treadmill (Ergosprint, Ergoline, Germany), separated by 7-14 days and conducted at the same time of day (±2 hours) to control for circadian effects. The randomized order minimized potential order effects and ensured that fatigue from the first test did not systematically bias results.

Cardiopulmonary Exercise Testing Protocol Gas Exchange Measurement and Safety Monitoring Breath-by-breath gas exchange was measured using a metabolic cart (Vmax Encore, CareFusion, USA), calibrated before each test with standard gases and a 3-L calibration syringe. Heart rate was monitored continuously via 12-lead electrocardiography (Cardiosoft, GE Healthcare, USA), providing greater temporal resolution than telemetric methods. Blood pressure was measured at rest and every 2 minutes during exercise to monitor safety and detect cardiovascular abnormalities.

Unified Ramp Protocol The central innovation was implementing a unified ramp protocol on both modalities to eliminate kinetic confounding.

Cycle Ergometer: Following a 3-minute unloaded warm-up (0 W), continuous ramp increases began at 20 W·min-¹ (men) or 15 W·min-¹ (women), targeting an 8-12 minute test duration to optimize threshold identification within a physiologically relevant window.