Background: Accumulating research demonstrates that the timing of exercise plays an important role in influencing episodic memory. However, we have a limited understanding as to the factors that moderate this temporal effect. Thus, the purpose of this systematic review with meta-analysis was to evaluate the effects of study characteristics (e.g., exercise modality, intensity and duration of acute exercise) and participant attributes (e.g., age, sex) across each of the temporal periods of acute exercise on episodic memory (i.e., acute exercise occurring before memory encoding, and during memory encoding, early consolidation, and late consolidation). Methods: The following databases were used for our computerized searches: Embase/PubMed, Web of Science, Google Scholar, Sports Discus and PsychInfo. Studies were included if they: (1) Employed an experimental design with a comparison to a control group/visit, (2) included human participants, (3) evaluated exercise as the independent variable, (4) employed an acute bout of exercise (defined as a single bout of exercise), (5) evaluated episodic memory as the outcome variable (defined as the retrospective recall of information either in a spatial or temporal manner), and (6) provided sufficient data (e.g., mean, SD, and sample size) for a pooled effect size estimate. Results: In total, 25 articles met our inclusionary criteria and were meta-analyzed. Acute exercise occurring before memory encoding (d = 0.11, 95% CI: −0.01, 0.23, p = 0.08), during early memory consolidation (d = 0.47, 95% CI: 0.28, 0.67; p < 0.001) and during late memory consolidation (d = 1.05, 95% CI: 0.32, 1.78; p = 0.005) enhanced episodic memory function. Conversely, acute exercise occurring during memory encoding had a negative effect on episodic memory (d = −0.12, 95% CI: −0.22, −0.02; p = 0.02). Various study designs and participant characteristics moderated the temporal effects of acute exercise on episodic memory function. For example, vigorous-intensity acute exercise, and acute exercise among young adults, had greater effects when the acute bout of exercise occurred before memory encoding or during the early memory consolidation period. Conclusions: The timing of acute exercise plays an important role in the exercise-memory interaction. Various exercise- and participant-related characteristics moderate this temporal relationship.

To simultaneously examine the effects of acute exercise intensity and free-living physical activity and sedentary behavior on cognitive function in young, healthy adults. Using a counterbalanced, crossover, randomized controlled design, 87 young adults (mean age, 21.4 years) completed various cognitive assessments with and without an acute bout of exercise preceding the assessment. Participants were randomized into 1 of 4 groups to complete a 30-minute bout of acute exercise: control (no exercise), light intensity (40%-50% of predicted maximum heart rate [HR(max)]), moderate intensity (51%-70% of predicted HR(max)), or vigorous intensity (71%-85% of predicted HR(max)). Subjectively and objectively determined (accelerometry) physical activity and sedentary behavior were assessed to examine the association between these free-living behaviors and cognitive function. The study duration was August 26, 2013, to September 11, 2014. Concentration-related cognition (mean ± SD Feature Match test score) was significantly higher after a 30-minute acute bout of moderate-intensity exercise (145.1±26.9) compared with cognitive assessment without exercise (121.3±19.2; P=.004). Furthermore, questionnaire-determined sedentary behavior was inversely associated with visual attention and task switching (Trail Making Test A score) (β=-0.23; P=.04). Last, estimated cardiorespiratory fitness (volume of maximum oxygen consumption) was positively associated with reasoning-related cognitive function (Odd One Out test score) (β=0.49; P=.05); when adding metabolic equivalent of task minutes per week to this model, the results were not significant (β=0.47; P=.07). These findings provide some support for acute moderate-intensity exercise, sedentary behavior, and cardiorespiratory fitness being associated with executive functioning-related cognitive function in young, healthy adults.

Objective: To systematically summarize the experimental effects of exercise on cognitive-related memory function among young to middle-aged adults, which has yet to be done in the literature. Data Source: PubMed. Study Inclusion and Exclusion Criteria: Studies were included if they were published in the English language, indexed in PubMed, employed an experimental study design (eg, traditional parallel group randomized controlled trial: either acute intervention or chronic/training intervention study), and conducted among human adults. Studies were excluded if nonhumans (ie, animal models) were studied, if children/adolescents (50 years) were evaluated, and if select chronic diseases (eg, diabetes and dementia) were present. Data Extraction: A systematic review approach was employed. Data Synthesis: An extraction table was created synthesizing the key results, and recommendations for future research are emphasized. Results: Among the 17 evaluated studies, 2 were published before the year 2000 (ie, 1998 and 1999), 2 were published in 2007, and the remaining 13 were published in the years 2011 and beyond. This highlights the emergence of this research topic within this age-group (young to middle-aged adults). Among the 17 evaluated studies, 14 were conducted among healthy samples, with 3 conducted among those with a diagnosis of depression. Among the 17 studies, 4 employed a chronic training protocol, with 13 utilizing an acute exercise protocol. Among the 3 experimental studies in the depressed population, all demonstrated a favorable effect of exercise on memory function. Among the 14 trials in the nondepressed population, 10 (71%) demonstrated a favorable effect of exercise on some aspect of memory function. Conclusion: Acute and chronic exercise appears to play a pronounced effect on memory function among young to middle-aged adults. Implications and recommendations for future research are outlined in this systematic review.