# 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 PMID: 32102667 Journal: The international journal of behavioral nutrition and physical activity Published: 2020 Feb 26 Authors: Jung ME, Locke SR, Bourne JE, Beauchamp MR, Lee T, Singer J, MacPherson M, Barry J, Jones C, Little JP ## 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. ## Population - Ninety-nine previously low-active adults with overweight or obesity, aged 30-65 years, cleared for vigorous exercise. - Sample size: 99 - Age: Mean 50.9 years (SD 9.40); eligible age range 30-65 years. - Sex: 28 male, 69 female, 2 did not answer. - Fitness level: Low active; baseline relative VO2 about 22.81 mL/kg/min. - Health status: Overweight/obesity, BMI 25-40 kg/m2, cleared for vigorous exercise. ## Methodology - Two-arm parallel-group randomized trial with a 2-week supervised exercise counselling phase and 12 months of free-living follow-up. - 2-week supervised/counselling phase plus 12-month free-living follow-up - Initial sessions in laboratory and home settings; follow-up exercise was free-living with mobile-app self-monitoring and monthly booster messages. - Randomized and controlled study design. ## Protocol - HIIT plus brief behavior-change counselling. - Modality: 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. - Sets or repetitions: Progressed from 4 to 10 intervals; target 10 intervals. - Intensity: About 80-90% VO2peak during intervals; recovery about 40% VO2peak. - Session duration: About 25 minutes for full HIIT session including 5-minute warm-up and 5-minute cool-down. - Frequency: 3 times per week. - Program length: 12 months free-living after 2-week supervised/counselling phase. - Progression: 10 initial sessions over 2 weeks progressed from 4 to 10 intervals. - MICT plus brief behavior-change counselling. - Modality: Self-selected aerobic exercise modalities. - Work intervals: Continuous moderate-intensity exercise. - Intensity: About 45-55% VO2peak. - Session duration: Progressed from 20 to 50 minutes; target 50 minutes. - Frequency: 3 times per week. - Program length: 12 months free-living after 2-week supervised/counselling phase. - Progression: 10 initial sessions over 2 weeks progressed from 20 to 50 minutes. ## Outcomes ### Cardiorespiratory fitness Status: improved 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+ Status: mixed 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 Status: improved 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 Status: mixed 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. ## Practical 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 And Adherence - Participants were screened with PAR-Q+ and cleared for vigorous exercise. - No adverse events were reported in the extracted article text. ## Original Sources - [PubMed](https://pubmed.ncbi.nlm.nih.gov/32102667/) (pubmed) - [DOI](https://doi.org/10.1186/s12966-020-00933-8) (doi) - [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7045584/) (full text) ## Agent Guidance Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.