# Working memory improvements following supramaximal high-intensity interval training predicted by increased prefrontal cortex activation and leg strength gains

PMID: 41092049
Journal: Cerebral Cortex (New York, NY)
Published: 2025-10-14
Authors: Sandström S, Simonsson E, Hedlund M, Rosendahl E, Boraxbekk CJ

## Question

Do exercise-induced changes in cardiorespiratory fitness or leg strength explain changes in working-memory-related brain activation and working-memory performance after supramaximal HIT in older adults?

## Summary

This fMRI substudy of the Umea HIT randomized trial examined non-exercising older adults assigned to supramaximal HIT or moderate-intensity cycling. In the MRI sample, HIT did not significantly outperform moderate training on working-memory change, but HIT showed within-group working-memory gains, and leg-strength gains predicted increased right dorsolateral prefrontal cortex activation, which predicted in-scanner working-memory improvement. The imaging results were exploratory and uncorrected.

## Population

- MRI subsample of non-exercising older adults from the Umea HIT RCT.
- Sample size: 43
- Age: 66-79 years
- Sex: Approximately 56% female
- Fitness level: No regular moderate- or high-intensity exercise during the past year.
- Health status: Relatively healthy; cognitively intact by MMSE threshold and medically screened.

## Methodology

- Task-based fMRI substudy of a randomized controlled trial comparing supramaximal HIT with moderate-intensity training.
- 12 weeks
- Umea HIT study in Sweden with stationary-bicycle training and laboratory/MRI testing.
- Randomized and controlled study design.

## Protocol

- Watt-controlled supramaximal HIT.
- Modality: Stationary cycling.
- Work intervals: 6 s.
- Recovery: Not specified in this article.
- Sets or repetitions: 10 intervals.
- Intensity: Supramaximal watts above individual VO2peak wattage.
- Session duration: 20 min.
- Frequency: 2 sessions/week.
- Program length: 12 weeks.
- Progression: Individualized from baseline testing.
- Moderate-intensity training.
- Modality: Stationary cycling.
- Work intervals: 8 min bouts.
- Sets or repetitions: 3 bouts.
- Intensity: Moderate intensity individualized from baseline testing.
- Session duration: 40 min.
- Frequency: 2 sessions/week.
- Program length: 12 weeks.
- Progression: Individualized from baseline testing.

## Outcomes

### Working-memory performance
Status: mixed
Between-group change was not significant in the MRI sample, but HIT improved within-group offline and MRI WM composites.

Offline WM group x time p=0.15; MRI WM p=0.07; HIT within-group p=0.034 and p=0.008.

### Leg strength
Status: improved
HIT showed greater isometric leg-strength change than MIT and significant within-group improvement.

Between-group MD 0.08 Nm/kg, 95% CI 0.00 to 0.16, p=0.06; HIT within-group p=0.006.

### VO2peak
Status: improved
Both groups improved VO2peak with no significant between-group difference.

Mean increase 1.49 ml/kg/min, 95% CI 0.76 to 2.21; between-group p=0.32.

### fMRI activation mechanism
Status: mixed
In HIT only, strength gains predicted increased right dlPFC activation, and dlPFC activation predicted in-scanner WM improvement; VO2peak did not predict activation.

Strength to dlPFC beta 0.87 p=0.022; dlPFC to performance beta 4.08 p=0.012; uncorrected fMRI threshold p<0.001.

## Practical Insights

- Cognitive benefit claims from HIIT should be conservative and mechanism-focused.
- Leg strength may be a relevant mediator, so combined HIIT plus lower-body strength programming is plausible.
- Exploratory fMRI findings should not be surfaced as definitive user-facing health claims.

## Limitations

- Small MRI subsample
- Uncorrected exploratory fMRI analyses
- No significant between-group WM change in MRI sample
- No long-term follow-up
- Healthy and relatively well-educated older adults

## Safety And Adherence

- No adverse-event or injury data were reported in this article.
- Participants were screened for medical, cognitive, and MRI contraindications.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/41092049/) (pubmed)
- [DOI](https://doi.org/10.1093/cercor/bhaf277) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12526879/) (full text)

## Agent Guidance

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