# High intensity interval training in a real world setting: a randomized controlled feasibility study in overweight inactive adults, measuring change in maximal oxygen uptake PMID: 24454698 Journal: PloS one Published: 2014-01-13 Authors: Lunt H, Draper N, Marshall HC, Logan FJ, Hamlin MJ, Shearman JP, Cotter JD, Kimber NE, Blackwell G, Frampton CM ## Question Can aerobic interval training or maximal volitional interval training improve VO2max with less exercise time than walking in overweight, inactive adults exercising in a low-cost real-world community setting? ## Summary This pragmatic 12-week randomized feasibility trial tested whether two outdoor, community-park HIIT formats could improve VO2max in overweight, inactive adults while requiring less exercise time than a walking program. Aerobic interval training produced a modest VO2max advantage versus walking on intention-to-treat analysis, while maximal volitional interval training did not. The paper strongly emphasizes that adherence, injuries, and real-world delivery constraints reduced the apparent effect compared with more controlled laboratory HIIT studies. ## Population - Overweight or obese inactive adults recruited from the community and host institutions; eligible participants were 35-60 years old, BMI 28-40 kg/m2, and doing less than 2 x 30 minutes of moderate activity weekly. - Sample size: 49 - Age: 35-59 years randomized; mean age by ITT group 46.3 years WALK, 48.2 years AIT, 50.3 years MVIT. - Sex: 36 female and 13 male overall; group splits WALK 5M/12F, AIT 4M/12F, MVIT 4M/12F. - Fitness level: Inactive with low cardiorespiratory fitness; mean baseline VO2max 25.3 +/- 4.5 ml/min/kg. - Health status: BMI range 27.7-39.3 kg/m2; many had cardiometabolic risk features, 2 participants had type 2 diabetes, 10 used antidepressants, 7 used cardiovascular risk-reduction medications. ## Methodology - Randomized controlled feasibility trial with three parallel exercise groups: walking active control, aerobic interval training, and maximal volitional interval training. - 12 weeks - Outdoor group exercise sessions in Hagley Park, Christchurch, New Zealand, during Autumn/Winter evenings. - Randomized and controlled study design. ## Protocol - Aerobic interval training and maximal volitional interval training. - Modality: AIT fast walking/jogging; MVIT maximal uphill walking/jogging. - Work intervals: AIT 4 minutes; MVIT 30 seconds progressing toward 45 seconds. - Recovery: AIT 3 minutes walking pace; MVIT 4 minutes walking recovery. - Sets or repetitions: AIT 4 repetitions; MVIT 3 repetitions initially progressing toward 6. - Intensity: AIT 85-95% HRmax; MVIT all-out maximal volitional effort. - Session duration: AIT 40 minutes including 10-minute warmup and 5-minute cooldown; MVIT 24.5 to 40 minutes including warmup/cooldown. - Frequency: 3 sessions/week. - Program length: 12 weeks. - Progression: AIT maintained HR target as fitness improved; MVIT progressed repetitions and interval duration until injury-triggered halt in weeks 11-12. - Walking active control. - Modality: Walking. - Work intervals: 33 minutes continuous moderate walking. - Sets or repetitions: 1 continuous walking bout. - Intensity: 65-75% HRmax. - Session duration: 48 minutes including 10-minute warmup and 5-minute cooldown. - Frequency: 3 sessions/week. - Program length: 12 weeks. - Progression: Heart-rate based; participants had to work harder over time to remain in the HR zone. ## Outcomes ### VO2max Status: mixed On ITT analysis, AIT improved VO2max more than WALK, while MVIT did not. Baseline/exit VO2max was AIT 24.2 +/- 4.8 to 25.6 +/- 4.8, MVIT 25.0 +/- 2.8 to 25.2 +/- 3.4, WALK 26.5 +/- 5.3 to 25.2 +/- 3.6. ITT change: AIT +1.01, MVIT -0.06, WALK -1.03 ml/min/kg; AIT versus WALK p=0.027, MVIT versus WALK p=0.27. PP AIT versus WALK p=0.096. ### Exercise time and adherence Status: mixed AIT and MVIT required less actual weekly exercise time than walking but adherence was lower, especially in AIT. Actual mean weekly exercise time ITT: WALK 116 minutes, AIT 74 minutes, MVIT 45 minutes; p<0.001 for HIIT comparisons. Attendance: WALK 75%, AIT 59%, MVIT 75%. ### Secondary body composition and cardiometabolic outcomes Status: mixed Across the whole cohort, waist circumference, body fat, blood pressure, and total cholesterol improved, but between-group comparisons did not show clear HIIT superiority for these outcomes. Examples from Table 3 ITT total group: waist circumference p<0.001, body fat p<0.001, systolic BP p=0.001, total cholesterol p=0.025; Table 5 group contrasts mostly nonsignificant. ### Safety Status: worse/safety concern Higher-intensity groups showed more injury concern than walking; MVIT progression was halted after three intervention-related injuries at week 10. Descriptive analysis: walking subgroup had the fewest adverse events; no inferential adverse-event statistics reported in main text. ## Practical Insights - Real-world HIIT effectiveness depends heavily on adherence, not just protocol efficacy. - For inactive overweight adults, submaximal HR-prescribed intervals may be safer and more useful than all-out uphill efforts. - Warmup, cooldown, and recovery periods can erode HIIT's time-saving promise; app summaries should separate hard-work time from full session time. - Injury-sensitive progression, exercise variation, and surface/lighting constraints should be included in practical programming guidance. ## Limitations - Small feasibility trial with wide confidence intervals. - High screen failure and attrition. - Low adherence in HIIT groups, especially AIT. - Outdoor park setting, weather, surface, and artificial illumination may limit generalizability and affect injury risk. - Participants were overweight/inactive adults with cardiometabolic risk, not a general healthy fitness population. - Diet was not changed by design, but dual diet plus exercise interventions may be more relevant for many health outcomes. ## Safety And Adherence - Walking had the fewest adverse events on descriptive analysis. - Three MVIT participants developed injuries considered related to intervention intensity by week 10, causing planned weeks 11-12 progression to be cancelled. - One participant missed exit VO2max because of exercise-related injury; the paper also notes minor exercise-related injuries led to temporary reductions in exercise intensity. - Authors suggest injuries may have been minimized by a different venue, more gradual intensity progression, and greater activity variation. ## Original Sources - [PubMed](https://pubmed.ncbi.nlm.nih.gov/24454698/) (pubmed) - [DOI](https://doi.org/10.1371/journal.pone.0083256) (doi) - [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3890270/) (full text) ## Agent Guidance Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.