# The Mediation Role of Fatness in Associations between Cardiorespiratory Fitness and Blood Pressure after High-Intensity Interval Training in Adolescents

PMID: 35162721
Journal: International Journal of Environmental Research and Public Health
Published: 2022-02-01
Authors: Domaradzki J, Koźlenia D, Popowczak M

## Question

Do fatness measures mediate the association between baseline cardiorespiratory fitness and post-HIIT resting blood pressure in adolescents, and does sex moderate this mediation?

## Summary

This secondary analysis of a school-based HIIT intervention found that, among non-hypertensive adolescents who completed the HIIT arm, better baseline cardiorespiratory fitness was associated with lower post-intervention systolic blood pressure. In boys, body fat mass and fat mass index statistically mediated that relationship; in girls, the relationship appeared independent of fatness. The study does not test HIIT versus control effects directly.

## Population

- Non-hypertensive adolescents who participated in the HIIT intervention arm.
- Sample size: 64
- Age: Boys 16.17 ± 0.30 years; girls 16.11 ± 0.39 years.
- Sex: 28 boys and 36 girls.
- Fitness level: Very poor cardiorespiratory fitness by Harvard Step Test fitness index.
- Health status: Non-hypertensive, normal-range BMI and body fat; hypertensive adolescents were excluded for this analysis.

## Methodology

- Prospective mediation analysis of the experimental HIIT arm from a school-based intervention project.
- 10-week HIIT intervention with pre/post measurements.
- Secondary school physical education setting in Wroclaw, Poland.

## Protocol

- PE Tabata HIIT.
- Modality: Bodyweight Tabata-style exercises during PE lessons.
- Work intervals: 20 seconds.
- Recovery: 10 seconds.
- Sets or repetitions: Three 4-minute Tabata cycles, each with 8 rounds; 1-minute breaks between cycles.
- Intensity: 75-80% HRmax, 145-157 bpm based on Tanaka formula for age 16.
- Session duration: 10-minute warm-up plus 14-minute HIIT block.
- Frequency: 1 session per week.
- Program length: 10 weeks.
- Progression: No explicit progression; video timing used to implement work and rest accurately.

## Outcomes

### CRF and SBP
Status: improved
Higher baseline CRF was associated with lower post-intervention systolic blood pressure in both sexes.

Boys B = -0.603, p = 0.010; girls B = -0.394, p = 0.037.

### CRF and DBP
Status: no clear change
Baseline CRF was not significantly associated with post-intervention diastolic blood pressure.

Boys B = -0.055, p = 0.829; girls B = -0.184, p = 0.373.

### Fatness mediation
Status: mixed
Body fat mass and fat mass index mediated the CRF-SBP relationship in boys but not girls; BMI did not mediate in either sex.

Boys BFM paths: CRF→BFM p = 0.009, BFM→SBP p = 0.009, direct CRF→SBP p = 0.076. Boys FMI paths: CRF→FMI p = 0.029, FMI→SBP p = 0.007, direct p = 0.057.

### Sex moderation
Status: mixed
Sex moderated mediation models, so analyses were conducted separately for boys and girls.

Moderation interactions were identified in nearly each model except BFM as mediator for DBP.

## Practical Insights

- Baseline fitness and fatness may influence adolescent blood pressure response after HIIT.
- BMI may be less sensitive than body fat mass or fat mass index for explaining adolescent BP relationships.
- This is explanatory mediation evidence and should not be used as a direct HIIT efficacy estimate.

## Limitations

- Small sample.
- No control group in this analysis.
- Only 16-year-old adolescents from one school project.
- Not nationally representative of Polish youth.
- Lifestyle covariates such as nutrition, smoking, and physical activity were not included.
- CRF was estimated using a field test rather than VO2max.

## Safety And Adherence

- This analysis did not report new adverse events.
- The parent HIIT project used safe school-based intensity and excluded adolescents with hypertension for this mediation analysis.
- The paper states the effort intensity was safe to avoid side effects such as dizziness or faintness.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/35162721/) (pubmed)
- [DOI](https://doi.org/10.3390/ijerph19031698) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8834818/) (full text)

## Agent Guidance

Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.