Acute hemodynamic responses to high intensity interval training, moderate intensity continuous training, and vigorous intensity continuous training in active men

Introduction: Cardiac output (CO), the product of heart rate and stroke volume (SV), reflects oxygen transport to skeletal muscle during exercise and is a determinant of maximal oxygen uptake (VO2max). This study assessed differences in the CO and SV response to three duration-matched sessions of cycling. Methods: Eighteen healthy non-obese men (age and VO2max = 24 ± 5 yr and 41 ± 9 mL/kg/min) initially completed incremental cycling to exhaustion to determine VO2max, maximal CO and SV, and first ventilatory threshold (VT1). Subsequent sessions included 15 min of high intensity interval training (HIIT) at workload equal to 30% above VT1, moderate intensity continuous training (MICT) at 30% below VT1, and vigorous intensity continuous training (VICT) at 10% below VT1. Pulmonary gas exchange data and thoracic impedance were used to assess changes in VO2, SV, arterio-venous oxygen difference (avO2diff), and CO during exercise. Results: Results revealed significantly higher mean VO2 in response to VICT versus HIIT (2.43 ± 0.52 vs. 2.25 ± 0.39 L/min, p = 0.016, d = 0.69) which was associated with a significantly higher (p = 0.01) avO2diff (12.4 ± 2.0 vs. 11.4 ± 1.6 mL/dL, d = 0.37), yet CO was similar (p > 0.05) between VICT and HIIT. Stroke volume was not different across protocols (p = 0.08) and displayed varied responses across participants. Conclusions: Despitelower intensity than HIIT, VICT elicited significantly higher mean VO2 and similar CO compared to HIIT, suggesting a substantial stimulus on the cardiovascular system during exercise.