# Effect of high-intensity interval training on hippocampal metabolism in older adolescents

PMID: 35599295
Journal: Psychophysiology
Published: 2022 Nov
Authors: Valkenborghs SR, Hillman CH, Al-Iedani O, Nilsson M, Smith JJ, Leahy AA, Harries SK, Ramadan S, Lubans DR

## Question

Does a school-based HIIT intervention change hippocampal metabolites in lower-fit older adolescents, and are those changes associated with fitness and working-memory outcomes?

## Summary

In a cluster-randomized school study of lower-fit older adolescents, a 16-week teacher-led HIIT program increased left hippocampal NAA and Glx metabolite concentrations compared with control. Changes in these metabolites were associated with improvements in cardiorespiratory fitness, lower-body muscular fitness, and working memory, but the outcomes were mechanistic surrogate brain measures in a small school sample.

## Population

- Lower-fit older adolescents from 10 classes in 4 government secondary schools.
- Sample size: 56
- Age: 16.1 +/- 0.4 years
- Sex: 61% female overall
- Fitness level: Lower-fit adolescents selected from the bottom 50% of baseline cardiorespiratory fitness
- Health status: Lower-fit older adolescents from government secondary schools

## Methodology

- Substudy of a cluster-randomized controlled trial
- 16-week intervention with 6-month follow-up assessment
- Government secondary schools in New South Wales, Australia
- Randomized and controlled study design.

## Protocol

- Burn 2 Learn school HIIT.
- Modality: Teacher-led aerobic and bodyweight resistance HIIT during academic lessons.
- Work intervals: Varied brief HIIT formats delivered through the Burn 2 Learn program.
- Recovery: Varied by session.
- Sets or repetitions: Varied by session.
- Intensity: Students were encouraged to reach at least 85% of age-predicted HRmax using the app and heart-rate monitors.
- Session duration: 8-20 minutes including warm-up and cool-down.
- Frequency: At least 2 sessions per week requested; actual school completion averaged 2.9 +/- 0.7 sessions per week.
- Program length: 16 weeks.
- Progression: Program delivered through teacher training, resources, student app support, and heart-rate monitoring.
- Control.
- Modality: Usual school classes without the Burn 2 Learn HIIT intervention.
- Program length: 16 weeks.

## Outcomes

### Main reported result
Status: unclear
Forty-eight of 56 participants completed the 6-month assessment.

### Main reported result
Status: unclear
The intervention produced group-by-time effects on left hippocampal NAA, mean difference 2.66 mmol/L, 95% CI 0.20 to 5.11, d = 0.66.

### Main reported result
Status: unclear
The intervention produced group-by-time effects on left hippocampal Glx, mean difference 3.38 mmol/L, 95% CI 0.34 to 6.42, d = 0.67.

### Main reported result
Status: mixed
Increases in left hippocampal NAA and Glx were associated with improvements in cardiorespiratory fitness, lower-body muscular fitness, and working memory in the intervention group.

### Main reported result
Status: unclear
No associations were observed with the other secondary outcomes reported.

## Practical Insights

- Brief 8-20 minute HIIT sessions can be embedded into school lessons with teacher training and app support.
- Heart-rate feedback was used to cue a target intensity of at least 85% age-predicted HRmax.
- Brain-metabolite outcomes should be presented as mechanistic evidence rather than direct health or performance outcomes.

## Limitations

- Small homogeneous school sample.
- Cluster rather than individual randomization.
- Magnetic resonance spectroscopy voxel-positioning differences and partial-volume contamination were possible.
- Fitness measures were field tests rather than laboratory gold standards.
- The study could not scan the prefrontal cortex because of time constraints.

## Safety And Adherence

- Adverse events were not reported in the extracted full-text sections.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/35599295/) (pubmed)
- [DOI](https://doi.org/10.1111/psyp.14090) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9787522/) (full text)

## Agent Guidance

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