PMID 42111159

Research
All papers

Weekly frequency of school-based HIIT improves adiposity and fitness in children with obesity

Gao Y, Cao M, Xie Y, Zhou Y, Zhang T, Wang C, Wang X

Question

Does weekly frequency of the same school-based HIIT protocol produce different effects on BMI-z, adiposity, and cardiorespiratory fitness in children with obesity?

Summary

This 12-week school-based randomized trial compared the same short running HIIT protocol performed once, twice, or three times per week against usual physical education in children with obesity. All HIIT frequencies improved shuttle-run fitness versus control, while two or three weekly sessions produced stronger adiposity-related improvements than one weekly session. The protocol was short, embedded into PE classes, highly attended, and reported no training-related injuries.

Methodology

  • Children aged 10-12 years with obesity, Tanner stage II, BMI at or above the 95th percentile, enrolled in regular school PE, and self-reported physical activity under 2 hours/week.
  • 60 participants.
  • Running-based HIIT on school track or field.
  • Work intervals: 15 seconds at individualized target distance corresponding to 100% maximal aerobic speed.
  • Recovery: 15 seconds recovery corresponding to 50% maximal aerobic speed, returning to a common start line.
  • Intensity: Target 80-90% age-predicted HRmax during work intervals; live HR monitoring supported fidelity and safety.
  • Approximately 16-minute HIIT segment: 5-minute warmup, 6-minute HIIT, 5-minute cooldown, embedded in a 40-minute PE class.
  • 1, 2, or 3 sessions/week depending on group, on non-consecutive days whenever possible.
  • 12 weeks.
  • 12-week four-arm parallel-group randomized controlled trial with 2-week baseline lead-in; control, 1x/week HIIT, 2x/week HIIT, and 3x/week HIIT.
  • BMI-z, Body composition, 20mSRT performance and estimated VO2max, and Blood pressure were tracked.

Outcomes

Adiposity

BMI and BMI-z decreased over time, and ANCOVA showed 2x/week and 3x/week HIIT produced greater BMI and BMI-z reductions than control; 2x/week and 3x/week also reduced BMI, BMI-z, and fat mass more than 1x/week in change-score comparisons.

Time effects BMI p=0.002 partial eta2=0.092, BMI-z p=0.002 partial eta2=0.097; MFG and HFG vs CG all p<0.05 for BMI/BMI-z; MFG and HFG vs LFG p<0.0125 for BMI, BMI-z, and FM.

Improved

Body composition secondary measures

Body fat percentage and fat mass showed time effects but did not meet the predefined significance threshold; VAT was exploratory; some outcomes suggested attenuated returns beyond once weekly.

BF% p=0.033 partial eta2=0.046 and FM p=0.028 partial eta2=0.049 did not meet predefined threshold; no significant group x time interactions for BMI, BMI-z, BF%, FM, VAT, or FFM.

Mixed

Cardiorespiratory fitness

All HIIT groups improved 20mSRT-derived fitness compared with control, but differences among HIIT frequencies were small, with diminishing incremental gains from two to three sessions/week.

Estimated VO2max group effect p<0.001 partial eta2=0.204; time effect p<0.001 partial eta2=0.242; group x time interaction p=0.129; post hoc all HIIT groups vs CG p<0.05; frequency-response linear fit R2 approximately 0.63.

Improved

Safety and adherence

The short school-based protocol was feasible with high adherence and no training-related injuries or adverse events.

Adherence exceeded 90% in all HIIT groups; no training-related injuries/adverse events reported; overall completion rate 85%.

Improved

Insights

  • A very compact 6-minute interval block can fit inside a 16-minute warmup-to-cooldown segment within a normal 40-minute PE class.
  • For youth with obesity, once-weekly HIIT may be enough for fitness improvement, while two or more weekly sessions may be needed when adiposity improvement is the goal.
  • Make-up sessions and embedding HIIT into an existing class structure may be important adherence supports.
  • Live HR feedback and adult supervision were part of the safety model; unsupervised translation should be more cautious.

Limitations

  • Modest sample from a single region, limiting generalizability and power for secondary and sex-specific outcomes.
  • 12-week duration may not reveal longer-term divergence across frequencies or durability after the program.
  • Dietary intake and physical activity outside PE were not objectively monitored at the individual level.
  • Training HR logs were not exported or retained in analyzable format, and RPE was not collected.
  • Estimated VO2max was based on field shuttle-run equations rather than direct cardiopulmonary testing.
  • Body composition measures were not gold-standard DXA or imaging-based measures.

Safety

  • No training-related injuries or adverse events were reported.
  • Any discomfort during training was evaluated immediately by the school physician and on-site medical personnel.
  • Two moderate-frequency-group participants withdrew after a non-training ankle sprain while walking downstairs after class.
  • Eligibility excluded contraindications to vigorous exercise and medication or health risks that could affect exercise or metabolism.