PMID 24454698

Research
All papers

High intensity interval training in a real world setting: a randomized controlled feasibility study in overweight inactive adults, measuring change in maximal oxygen uptake

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.

Methodology

  • 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.
  • 49 participants.
  • 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.
  • Intensity: AIT 85-95% HRmax; MVIT all-out maximal volitional effort.
  • AIT 40 minutes including 10-minute warmup and 5-minute cooldown; MVIT 24.5 to 40 minutes including warmup/cooldown.
  • 3 sessions/week.
  • 12 weeks.
  • Randomized controlled feasibility trial with three parallel exercise groups: walking active control, aerobic interval training, and maximal volitional interval training.
  • VO2max, Exercise adherence and time spent exercising, Body composition and cardiometabolic secondary outcomes, and Adverse events and exercise-related injuries were tracked.

Outcomes

VO2max

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.

Mixed

Exercise time and adherence

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%.

Mixed

Secondary body composition and cardiometabolic outcomes

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.

Mixed

Safety

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.

Safety concern

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

  • 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.