The Temporal Effects of Acute High-Intensity Exercise on Semantic Memory and Potential Moderating Effects of Lactate

Abstract

Evidence suggests a single session of high-intensity aerobic exercise positively impacts memory. However, it is unclear whether exercising before or after learning provides the most benefit for memory enhancement. Therefore, this study aimed to determine the optimal timing of a single session of high-intensity exercise on long-term memory, with consideration for the possible moderating effects of peripheral lactate levels and cardiovascular fitness. Employing between-subject design, sixty males and females (mean age 27  8 years) were randomly assigned to one of three groups: running after encoding (run-after), running prior to encoding (run-before), or stretching before encoding (stretch-before). The running protocol included three 2-minute intervals at a rate of perceived exertion (RPE) of 17 (“very hard”) on the Borg scale, interspersed with 60-seconds of recovery. The control group engaged in gentle stretching for the same duration. Semantic memory was evaluated with a paired associate learning (PAL) task where participants memorized two lists of paired words for immediate recall as well as recognition and cued recall after returning 48 hours later. Estimated aerobic capacity was determined via the Chester Step test. Peripheral lactate samples were taken from the fingertip at three time points: after the initial exercise, at baseline, and following the Chester Step test. ANOVA showed significant group differences on cued recall at 48 hours (F(2, 56) = 3.36, p = .042) with Tukey post hoc revealing that the run-after group recalled more words than the stretch-before group. Collapsing across groups, a Spearman correlation found post-exercise lactate positively correlated with performance on the cued recall test at 48 hours (rs(57) = .265, p = .042). Analysis of the 48-hr recognition test revealed no group differences and no correlations with lactate levels. Aerobic capacity did not explain performance on the memory tests or moderate the relationship between acute exercise and recall. Findings demonstrate benefit of short high-intensity exercise during the consolidation period to enhance long-term memory and indicate that lactate may moderate these effects. Since PAL tasks are hippocampal-dependent, findings further suggest that high-intensity interval training (HIIT) could be leveraged to offset cognitive decline or dementia. Results further offer practical value to anyone interested in improving memory– whether for occupational, educational, or personal reasons.