# The effect of 4 weeks of high-intensity interval training and 2 weeks of detraining on cardiovascular disease risk factors in male adolescents

PMID: 36855259
Journal: Experimental physiology
Published: 2023 Apr
Authors: Kranen SH, Oliveira RS, Bond B, Williams CA, Barker AR

## Question

What effect do 4 weeks of HIIT running and 2 weeks of detraining have on vascular function and traditional cardiovascular risk factors in adolescent boys?

## Summary

In healthy adolescent boys, 4 weeks of school-based running HIIT improved brachial artery flow-mediated dilation, a macrovascular function marker, but did not change microvascular function, body composition, glucose, insulin, or lipids. The vascular improvement was no longer present after 2 weeks without training. Attendance was excellent and no adverse events occurred, but the sample was small and male-only.

## Population

- Healthy male adolescents.
- Sample size: 19
- Age: 13.3 +/- 0.5 years
- Sex: Male only
- Fitness level: Mostly moderate-to-high cardiorespiratory fitness percentiles.
- Health status: Healthy; one control participant overweight.

## Methodology

- Randomized controlled training and detraining study.
- 4 weeks training plus 2 weeks detraining
- School sports hall training with laboratory assessments at the University of Exeter.
- Randomized and controlled study design.

## Protocol

- School running HIIT.
- Modality: Shuttle running.
- Work intervals: 1 min.
- Recovery: 75 s passive rest.
- Sets or repetitions: 8 intervals weeks 1-2, 10 intervals week 3, 12 intervals week 4.
- Intensity: 90% maximal aerobic speed.
- Session duration: About 18-26 min plus 1 min warm-up depending on week.
- Frequency: 3 sessions/week.
- Program length: 4 weeks.
- Progression: Interval count increased over the intervention.
- Usual activity control.
- Modality: Normal physical activity routine.
- Program length: 4 weeks plus 2-week matched assessment.

## Outcomes

### Flow-mediated dilation
Status: improved
FMD was significantly greater in TRAIN than CON after 4 weeks, but no longer significantly different after 2 weeks detraining.

Post F(15)=5.33, p=0.036, ES=0.49; detraining p=0.062.

### Microvascular function
Status: no clear change
No training effect was detected for peak reactive hyperemia.

p=0.821.

### Body composition and blood biomarkers
Status: no clear change
No between-group differences were observed after training for BMI, fat mass, fat-free mass, body fat percentage, glucose, insulin, cholesterol fractions, or TAG.

Body composition p>=0.14; biomarkers p>=0.18.

### Adherence and safety
Status: improved
All TRAIN participants completed 100% of sessions without adverse events.

## Practical Insights

- Short adolescent HIIT may need continued programming to preserve vascular benefits.
- A simple running protocol can be delivered before school lessons with strong adherence under supervision.
- Do not promise broad metabolic or body composition changes from only 4 weeks in healthy boys.

## Limitations

- Small sample
- Male adolescents only
- Short intervention
- Surrogate vascular outcome
- Some missing vascular/lipid data

## Safety And Adherence

- All TRAIN participants completed all sessions without adverse events.
- Two participants failed to complete the overall study due to illness or time constraints.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/36855259/) (pubmed)
- [DOI](https://doi.org/10.1113/EP090340) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10103894/) (full text)

## Agent Guidance

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