Effect of high-intensity interval training on hippocampal metabolism in older adolescents
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.
Methodology
- Lower-fit older adolescents from 10 classes in 4 government secondary schools.
- 56 participants.
- 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.
- Intensity: Students were encouraged to reach at least 85% of age-predicted HRmax using the app and heart-rate monitors.
- 8-20 minutes including warm-up and cool-down.
- At least 2 sessions per week requested; actual school completion averaged 2.9 +/- 0.7 sessions per week.
- 16 weeks.
- Substudy of a cluster-randomized controlled trial
- Hippocampal metabolites by 3T magnetic resonance spectroscopy: NAA, Glx, total creatine, total choline, and myo-inositol, 20 m multistage fitness test, Push-ups and standing long jump, and 2-back working memory were tracked.
Outcomes
Main reported result
Forty-eight of 56 participants completed the 6-month assessment.
Main reported result
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
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
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
No associations were observed with the other secondary outcomes reported.
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
- Adverse events were not reported in the extracted full paper sections.