# A randomized controlled trial of enhancing hypoxia-mediated right cardiac mechanics and reducing afterload after high intensity interval training in sedentary men PMID: 34131157 Journal: Scientific Reports Published: 2021-06-15 Authors: Huang YC, Hsu CC, Fu TC, Wang JS ## Question How do 6 weeks of high-intensity interval training versus moderate-intensity continuous training affect right cardiac mechanics during hypoxic exercise in sedentary men? ## Summary In young healthy sedentary men, 6 weeks of supervised cycle HIIT improved aerobic capacity more than moderate continuous cycling and produced favorable right-heart responses during a short hypoxic cycling stress test. The HIIT group showed lower pulmonary vascular resistance and right ventricular systolic pressure during hypoxic exercise, higher right ventricular ejection fraction, and improved right atrial reservoir/conduit function and right ventricular radial strain-rate measures. The study is mainly useful for protocol and cardiovascular-mechanism evidence because the population was narrow and the outcomes were laboratory echocardiographic measures under simulated altitude. ## Population - Young healthy sedentary nonsmoking men from Taiwan. - Sample size: 54 - Age: Mean age by group: 21.1, 21.3, and 21.9 years. - Sex: Male only - Fitness level: Sedentary; baseline VO2max about 34.5-35.1 mL/kg/min. - Health status: Healthy, with no cardiopulmonary or hematological risks reported. ## Methodology - Single-blinded, parallel-assignment randomized controlled trial with HIIT, MICT, and non-exercise control groups. - 6 weeks - University/testing-center exercise and laboratory hypoxia chamber in Taiwan; cycle training supervised by licensed physical therapists. - Randomized and controlled study design. ## Protocol - HIIT. - Modality: Stationary bicycle ergometer. - Work intervals: 3 minutes at 80% oxygen uptake reserve/heart-rate reserve. - Recovery: 3 minutes active recovery at 40% oxygen uptake reserve/heart-rate reserve. - Sets or repetitions: 5 cycles. - Intensity: 80% oxygen uptake reserve for work; 40% for recovery; HR target from baseline CPET. - Session duration: At least 33 minutes including 3-minute warm-up and 30-minute interval block; cooldown not specified. - Frequency: 5 days per week. - Program length: 6 weeks. - Progression: Workload adjusted continuously to maintain target HR; no separate progression schedule reported. - MICT and non-exercise control. - Modality: Stationary bicycle ergometer for MICT; no exercise for control. - Work intervals: MICT: continuous 30 minutes. - Recovery: Not applicable for continuous training. - Sets or repetitions: 1 continuous bout for MICT. - Intensity: MICT: sustained 60% oxygen uptake reserve/heart-rate reserve. - Session duration: 30-minute MICT training period plus similar warm-up/cooldown as HIIT; exact total not specified. - Frequency: 5 days per week for MICT; none for control. - Program length: 6 weeks. - Progression: Workload adjusted to maintain target HR; control maintained original diet and physical activity habits. ## Outcomes ### VO2max Status: improved HIIT increased VO2max from 34.5 +/- 1.3 to 46.8 +/- 2.1 mL/kg/min and improved more than MICT, which increased from 35.1 +/- 1.2 to 41.6 +/- 1.9 mL/kg/min; control changed from 34.6 +/- 1.3 to 35.1 +/- 1.0. P < 0.05 for pre-post and HIIT vs MICT/CTL markers in Table 1. ### Pulmonary vascular resistance during hypoxic exercise Status: improved HIIT reduced exercise PVR from 1.16 +/- 0.05 to 1.05 +/- 0.05 WU; MICT changed from 1.17 +/- 0.05 to 1.13 +/- 0.06; control remained 1.17 +/- 0.04 to 1.17 +/- 0.03. HIIT pre-post and compared with control marked P < 0.05 in Table 2. ### Right ventricular ejection fraction Status: improved HIIT increased RVEF from 59.5 +/- 6.0% to 69.1 +/- 2.8%; MICT and control showed smaller nonsignificant changes. HIIT pre-post marked P < 0.05 in Table 2. ### Right atrial and right ventricular mechanics Status: mixed HIIT improved RA reservoir/conduit function and selected radial strain-rate measures; longitudinal RV strain measures were less responsive. Multiple Table 3 and Table 4 comparisons marked P < 0.05; correlations for RVEF with RA reservoir r=0.60 P<0.05, RA conduit r=0.64 P<0.01, RV radial strain r=-0.70 P<0.01, and PVR r=-0.70 P<0.01 during hypoxic exercise. ## Practical Insights - Longer aerobic HIIT intervals can be structured as 3 minutes hard and 3 minutes easy for five rounds when using heart-rate guided cycling. - A 5-day-per-week, 6-week HIIT cycle program produced large VO2max gains in young sedentary men, but this is a high-frequency supervised protocol. - For consumer programming, the protocol is better adapted as a cardio interval template than copied directly, because direct replication depends on ergometer workload and HR reserve targets. ## Limitations - Small sample. - Male-only young healthy sedentary participants. - No long-term follow-up. - Right-heart outcomes were measured under hypoxic exercise stress and may not generalize to normal exercise settings. - Noninvasive PVR estimation. - MICT dose may have been insufficient for full hemodynamic adaptation. ## Safety And Adherence - No exercise-induced adverse effect was reported. - Training and CPET were monitored; participants were screened for cardiopulmonary and hematological risks. ## Original Sources - [PubMed](https://pubmed.ncbi.nlm.nih.gov/34131157/) (pubmed) - [DOI](https://doi.org/10.1038/s41598-021-91618-0) (doi) - [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8206117/) (full text) ## Agent Guidance Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.