Effectiveness of HIIT compared to moderate continuous training in improving vascular parameters in inactive adults
Question
Does individualized HIT improve vascular function parameters more than MCT in a greater proportion of physically inactive Latin-American adults?
Summary
This randomized clinical trial analysis compared 12 weeks of supervised treadmill high-intensity interval training with moderate continuous training in physically inactive Latin-American adults. HIT used 4 x 4-min intervals at 85-95% heart-rate reserve with 4-min recoveries; MCT used 30-35 min of continuous treadmill exercise at 60-75% heart-rate reserve. HIT produced more favorable changes in some vascular measures, especially pulse wave velocity and peak brachial artery diameter, while FMD improved numerically but not significantly versus MCT. No adverse events were reported and adherence was high, but the study was small, single-site, and lacked a non-exercise control group.
Methodology
- Physically inactive Latin-American adults aged 18-45 years with BMI 18-30 kg/m2 and without specified cardiometabolic or other excluded conditions.
- 21 participants.
- Fast walking/running on treadmill with deck incline adjusted.
- Work intervals: 4 min at 85-95% HRR, maintaining target zone for at least 2 min.
- Recovery: 4 min at 75-85% HRR.
- Intensity: 85-95% HRR work intervals; 75-85% HRR recoveries; speed and incline continuously adjusted.
- 38-42 min total exercise time including cool-down.
- 3 sessions/week.
- 12 weeks.
- Secondary randomized clinical trial analysis from the HIT-Heart Study comparing MCT versus HIT.
- Flow-mediated dilation, Pulse wave velocity, Augmentation index, and Non-responder prevalence were tracked.
Outcomes
Peak brachial artery diameter
Peak brachial artery diameter significantly increased in both groups, with between-group difference favoring HIT.
MCT +0.1 mm (SE 0.1), HIT +0.3 mm (SE 0.1); between-group difference 0.1 mm, 95% CI 0.0 to 0.3, P < 0.01.
Flow-mediated dilation
FMD decreased in MCT and increased in HIT, but the between-group difference was not statistically significant.
MCT -1.0% (SE 2.1, d=0.388 in abstract but table d=0.165), HIT +1.8% (SE 1.8, d=0.699 in abstract but table d=0.301); between-group difference 2.9%, 95% CI -3.0 to 8.8.
Pulse wave velocity
PWV changed favorably in HIT compared with MCT.
MCT +0.1 m/s (SE 0.2, d=0.087) and HIT -0.4 m/s (SE 0.2, d=0.497); between-group difference -0.4, 95% CI -0.2 to -0.7.
Non-responder prevalence
HIT had numerically fewer non-responders for FMD and PWV, but differences were not statistically significant.
FMD non-responders: MCT 66% (6 cases) vs HIT 36% (4 cases), P=0.157; PWV non-responders: MCT 77% (7 cases) vs HIT 45% (5 cases), P=0.114.
Adherence
Adherence was high and similar between groups.
MCT 98.7% (SD 3.7), HIT 98.4% (SD 2.8), group effect P=0.969.
Safety
No adverse events were reported.
Insights
- A supervised 4 x 4-min treadmill HIT protocol at 85-95% HRR can be delivered with high adherence in inactive adults.
- For vascular outcomes, HIIT effects may differ by marker: PWV improved significantly versus MCT, while FMD did not reach a significant between-group difference.
- Heart-rate monitoring and individualized treadmill adjustment were central to protocol fidelity.
- A consumer app version should use screening, conservative progression, and RPE/HR cues rather than assuming all users can tolerate high recovery intensities.
Limitations
- Small sample size.
- No true no-exercise control group, limiting causal interpretation.
- Single-site design.
- Lack of control over tobacco usage was identified by authors.
- Only limited vascular indices were assessed.
- Plasma nitric oxide, antioxidants, and cytokines were not measured.
- Sex distribution was not available in the extracted article text.
Safety
- No adverse events were reported over the course of the investigation.
- Participants were screened to exclude cardiovascular disease and related morbidities, diabetes, thyroid dysfunction, cancer, pregnancy, and smoking.
- Sessions were supervised with heart-rate monitoring.