Cardiorespiratory fitness and accelerometer-determined physical activity following one year of free-living high-intensity interval training and moderate-intensity continuous training: a randomized trial
Question
Does a brief exercise counselling program paired with HIIT produce different 6- and 12-month cardiorespiratory fitness and free-living physical activity outcomes than the same program paired with moderate-intensity continuous training in low-active adults with overweight or obesity?
Summary
In previously low-active adults with overweight or obesity, a 2-week supervised exercise and behavior-change program followed by 12 months of free-living exercise improved cardiorespiratory fitness in both HIIT and moderate continuous training groups. MICT produced more accelerometer-measured purposeful physical activity, but fitness improvements were similar despite the HIIT group being prescribed half as many exercise minutes.
Methodology
- Ninety-nine previously low-active adults with overweight or obesity, aged 30-65 years, cleared for vigorous exercise.
- 99 participants.
- Self-selected aerobic exercise modalities after initial exposure to stationary cycling, treadmill, elliptical, and outdoor walking.
- Work intervals: 1-minute high-intensity intervals.
- Recovery: 1-minute recovery/rest periods.
- Intensity: About 80-90% VO2peak during intervals; recovery about 40% VO2peak.
- About 25 minutes for full HIIT session including 5-minute warm-up and 5-minute cool-down.
- 3 times per week.
- 12 months free-living after 2-week supervised/counselling phase.
- Two-arm parallel-group randomized trial with a 2-week supervised exercise counselling phase and 12 months of free-living follow-up.
- Absolute and relative VO2peak, Peak power output, Purposeful MVPA10+, and Body composition were tracked.
Outcomes
Cardiorespiratory fitness
Both HIIT and MICT improved absolute and relative VO2peak and peak power, with no significant between-group differences.
Average 12-month absolute VO2peak: HIIT +0.15 L/min (95% CI 0.08 to 0.23, p<0.001), MICT +0.11 L/min (95% CI 0.05 to 0.18, p=0.001), between-group p=0.38; relative VO2peak between-group p=0.76.
Purposeful MVPA10+
Both groups increased MVPA10+ on average, but MICT accumulated more MVPA10+ than HIIT.
Average 12-month MVPA10+: HIIT +35.68 min/week (95% CI 17.22 to 54.14), MICT +68.60 min/week (95% CI 48.66 to 88.54), between-group difference -32.92 min/week, p=0.02.
Body composition
Waist circumference and body fat percentage improved in both groups, with no between-group differences; body mass did not change.
Average waist circumference change: HIIT -2.26 cm, MICT -4.28 cm, between-group p=0.13. Average body fat change: HIIT -1.33 percentage points, MICT -1.42, between-group p=0.87. Body mass between-group p=0.30.
Self-efficacy
Task self-efficacy improved in HIIT at 6 and 12 months and in MICT at 6 months, but self-regulatory efficacy did not significantly change.
No significant between-group differences in task or self-regulatory efficacy at 6 or 12 months.
Insights
- A 10 x 1-minute HIIT structure can be adapted for low-active adults if progressed and paired with behavior support.
- Lower prescribed HIIT time can produce similar fitness improvements to higher-volume MICT, but may not produce equal total activity volume.
- Consumer HIIT programs should expect mixed exercise behavior and should not force exclusive HIIT when moderate exercise supports adherence.
- Fitness and body-composition claims should be separated from weight-loss claims when diet is not addressed.
Limitations
- No no-treatment comparator.
- Self-selected exercise modality limited intensity estimation.
- Accelerometry imperfectly measures intermittent HIIT adherence and condition-specific intensity.
- 28% dropout rate.
- Purposeful MVPA adherence was not limited to assigned exercise intensity.
- Possible exercise intensity drift over 1 year.
- Diet was not assessed.
Safety
- Participants were screened with PAR-Q+ and cleared for vigorous exercise.
- No adverse events were reported in the extracted article text.