Similar cardiometabolic effects of high- and moderate-intensity training among apparently healthy inactive adults: a randomized clinical trial
Question
Does high-intensity interval training differ from steady-state moderate-intensity continuous training for improving metabolic syndrome risk factors and related cardiometabolic outcomes in apparently healthy physically inactive adults?
Summary
This small randomized trial compared 12 weeks of supervised treadmill high-intensity interval training with energy-matched moderate continuous training in physically inactive Colombian adults. Both groups improved or changed several cardiometabolic markers, but HIT produced a larger reduction in the continuous metabolic syndrome Z-score, while single risk-factor changes were not consistently superior to moderate training. No adverse events were reported.
Methodology
- Apparently healthy physically inactive Colombian adults, age 18-45 years, BMI 18-30 kg/m2.
- 20 participants.
- Treadmill fast walking or running with incline.
- Work intervals: 4 min at 85-95% peak HRR.
- Recovery: 4 min active rest at 65% peak HRR.
- Intensity: 85-95% peak HRR during work intervals.
- Variable by kcal/kg/week target; 16 min hard work plus active rests at full interval prescription.
- 3 sessions/week.
- 12 weeks.
- Randomized clinical trial comparing HIT with MCT over 12 weeks with baseline and post-intervention cardiometabolic assessments.
- MetS Z-score, Waist circumference, Blood pressure, and Fasting glucose were tracked.
Outcomes
MetS Z-score
MetS Z-score improved significantly in both groups, with a significant time by group difference favoring HIT.
MCT change 1.546 (1.575), P=0.009, ES=0.82; HIT change -1.249 (1.629), P=0.015, ES=0.55; between-group difference -2.795 (95% CI 1.276 to 4.311), time x group P=0.001.
Average number of cardiometabolic risk factors
Average risk factors decreased in MCT but not HIT, with no significant between-group difference.
MCT -0.133, P=0.040, ES=0.67; HIT 0.018, P=0.294, ES=0.14; between-group P=0.227.
Individual metabolic syndrome components
No consistent between-group superiority appeared for individual MetS risk factors. Mean blood pressure decreased in HIT, while waist circumference and triglycerides decreased in MCT.
Mean BP HIT P=0.019; WC MCT P=0.006; triglycerides MCT P=0.012; no significant time x group effects for these individual risk factors.
Fasting glucose
Fasting glucose increased significantly in both groups but remained in the healthy range.
MCT P=0.039, ES=0.19; HIT P=0.001, ES=0.29; between-group P=0.078.
Safety
No adverse events were reported.
Insights
- A supervised 4 x 4 min treadmill HIIT protocol can be completed by screened inactive adults with high session attendance.
- HIIT programming for inactive adults should include progression and monitoring rather than immediate full-dose unsupervised intensity.
- This study supports cautious claims about composite cardiometabolic risk, not broad superiority over moderate training for every risk factor.
Limitations
- No true non-exercise control group
- Small sample size
- Single-site design
- Baseline MetS Z-score differed between groups
- Bioelectrical impedance analysis was used for body composition and is not the gold standard
- Supervised treadmill setting limits translation to unsupervised app-based workouts
Safety
- No adverse events were reported over the course of the investigation.
- Participants with AHA absolute contraindications to exercise testing were excluded.
- Exercise sessions were supervised and heart rate monitored.