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

Physical exercise shows positive effects on cognitive functions such as working memory (WM) for older adults; however, large individual differences in response exist and the underlying mechanisms are not well understood. We tested the hypothesis that exercise-induced changes in cardiorespiratory fitness and leg strength would improve WM-related brain activity, which subsequently would improve WM performance. This study was based on the Umeå HIT study, a randomized controlled trial assessing the effects of watt-controlled supramaximal high-intensity interval training (HIT) versus moderate-intensity training for nonexercising older adults (N = 68). A subsample (n = 43, 66 to 79 years, 56% females) underwent task-based functional magnetic resonance imaging, testing WM. The outcomes of interest were change in WM performance, WM task activation, cardiorespiratory fitness, and leg strength. For WM performance, we found no significant between-group difference in change; however, there was a significant within-group increase for HIT in WM composites. For HIT, changes in leg strength significantly predicted increased right dorsolateral prefrontal cortex activation, which in turn predicted improved in-scanner WM task performance. Cardiorespiratory fitness did not predict WM-related functional change. These results indicate a specific physiological ingredient, namely leg strength gains, that is a potential mechanism in exercise-induced prefrontal activation and WM performance increases.