A randomized controlled trial of enhancing hypoxia-mediated right cardiac mechanics and reducing afterload after high intensity interval training in sedentary men

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.

Methodology

Young healthy sedentary nonsmoking men from Taiwan.
54 participants.
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.
Intensity: 80% oxygen uptake reserve for work; 40% for recovery; HR target from baseline CPET.
At least 33 minutes including 3-minute warm-up and 30-minute interval block; cooldown not specified.
5 days per week.
6 weeks.
Single-blinded, parallel-assignment randomized controlled trial with HIIT, MICT, and non-exercise control groups.
Right cardiac mechanics during hypoxic exercise, VO2max, Pulmonary vascular resistance, and Right ventricular ejection fraction were tracked.

Outcomes

VO2max

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.

Improved

Pulmonary vascular resistance during hypoxic exercise

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.

Improved

Right ventricular ejection fraction

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.

Improved

Right atrial and right ventricular mechanics

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.

Mixed

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

No exercise-induced adverse effect was reported.
Training and CPET were monitored; participants were screened for cardiopulmonary and hematological risks.