PMID 41092049

Research
All papers

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

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.

Methodology

  • MRI subsample of non-exercising older adults from the Umea HIT RCT.
  • 43 participants.
  • Stationary cycling.
  • Work intervals: 6 s.
  • Recovery: Not specified in this article.
  • Intensity: Supramaximal watts above individual VO2peak wattage.
  • 20 min.
  • 2 sessions/week.
  • 12 weeks.
  • Task-based fMRI substudy of a randomized controlled trial comparing supramaximal HIT with moderate-intensity training.
  • Offline working-memory composite, MRI working-memory composite, Working-memory brain activation, and VO2peak were tracked.

Outcomes

Working-memory performance

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.

Mixed

Leg strength

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.

Improved

VO2peak

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.

Improved

fMRI activation mechanism

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.

Mixed

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

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