Loprinzi et al.¹ conducted an experiment to evaluate the potential link between fitness/endurance and episodic memory performance and if there is influence from the post-exercise recovery period. The impetus for this study sprang from mixed findings in the previous literature on the association of cardiorespiratory fitness with general cognitive performance.

Cardiorespiratory endurance/fitness – The ability of the circulatory and respiratory systems to supply oxygen to the body and brain during sustained exercise. Often, it is measured by the amount of oxygen an individual can consume and utilize during a maximal graded exercise test.

Of note, Cole et al. 2020² showed for the first time that those with greater cardiorespiratory fitness were associated with larger hippocampal volume and were related to an enhanced rate of relational memory acquisition.

Primary Objective of Study

The primary objective was to study the effect that different intensities of exercise had on long-term episodic memory function and whether this is influenced by the post exercise recovery period. Basically: does exercise have an effect on memory function and if this effect is influenced by the amount of rest given after exercise.

Secondary Objective of Study

The secondary objective was to study if aerobic endurance/fitness (VO2max) influences the interaction between exercise intensity and the post-exercise recovery period on long-term episodic memory function.

Design of Study

59 participants split into three groups (mean age of 20) completed 12 primary laboratory visits. Each visit included a 20-min bout of exercise with varying degrees of intensity (control, moderate, and vigorous) followed by a recovery period (1, 5, 10, and 15 minutes) and then a word-list episodic memory task (involving an encoding phase and two long-term recall assessments – 20-min and 24-hr delayed recall). They included both a 20-min and 24-hr delayed recall memory assessment to allow them to determine if the time period post-encoding moderates the effects of acute exercise on long-term memory performance.

With this study a 3×4 factorial design was used. Meaning, 3 (exercise intensity: control, moderate, vigorous) x 4 (post-exercise recovery: 1-min post, 5-min post, 10-min post, 15-min post). Both factors of intensity and recovery length occurred as within subject factors.

In this context, “within-subject factors” means that each participant in the study experiences all levels of both factors (exercise intensity and post-exercise recovery time). So, for example, each participant would be exposed to the control, moderate, and vigorous exercise conditions, as well as all the recovery time points (1-minute, 5-minute, 10-minute, and 15-minute post-exercise).

This design allows the researchers to compare how the same individual responds to different conditions, controlling for individual differences, as each participant acts as their own control. This is useful because it reduces variability that might come from differences between people, making it easier to detect the effects of the factors being studied.

Results

The primary finding was that moderate and vigorous-intensity exercise improved memory function when compared to a non-exercise control. A secondary finding is that those with higher levels of aerobic endurance, had greater memory performance after exercise, when compared to their lesser fit counterparts.

Based on these results, the authors suggest that a 20-min bout of exercise, followed by a rest period of up to 15 minutes, may be sufficient to enhance long-term memory performance.

Proposed mechanism behind this effect

Aerobic exercise improves cognitive and motor function by inducing neuroplasticity. A systematic review by El-Sayes et al. studied the neural mechanisms that mediate exercise induced neuroplasticity. They found that acute exercise may alter molecular changes, such as increasing vascular endothelial growth factor and brain-derived neurotrophic factor (a key memory-related neurotrophin). These responses may lead to the functional responses of increased blood flow, glucose and oxygen metabolism, neurotransmitter release, and neural/receptor activity. These responses may work to increase memory function. Structural changes can occur also. Animal work with long-term potentiation via electrical stimulation can induce synaptic changes via increases in the size of dendritic spines within a few hours of the stimulus induction. Exercise may induce similar effects in humans.

1. Loprinzi PD, Roig M, Tomporowski PD, Javadi AH, Kelemen WL. Effects of acute exercise on memory: Considerations of exercise intensity, post-exercise recovery period and aerobic endurance. Mem Cognit. 2023;51(4):1011-1026. doi:10.3758/s13421-022-01373-4
2. Cole RC, Hazeltine E, Weng TB, et al. Cardiorespiratory fitness and hippocampal volume predict faster episodic associative learning in older adults. Hippocampus. 2020;30(2):143-155. doi:10.1002/hipo.23151