We analyzed our secondary data from a six-month intervention to examine the effects of aerobic training and resistance training on two distinct forms of memory. Our specific aims were to evaluate whether either type of exercise would improve verbal memory and learning and/or spatial memory and to determine whether an association might exist between postintervention memory performance and physical measures. In this regard, we report three key findings. First, we found that twice-weekly aerobic training for six months remembered significantly more items in the loss after interference condition on the verbal memory test. Second, our results suggest that both types of exercise improved reaction times during the spatial memory test compared to the control group. Last, spatial memory performance appears to be positively associated with physical performance in the aerobic training group after the intervention. The results of our present study extend those from our previous work [11
], where we found that resistance training significantly improved associative memory. Within this context, several noteworthy points of discussion follow.
To begin with, our finding that aerobic exercise significantly improved verbal memory and learning is consistent with previous reports. Specifically, Pereira and colleagues [30
] found that three months of aerobic exercise improved performance on the RAVLT. While the benefits of aerobic activity on verbal memory and learning in our study were only observed after six months—compared to three months in the study by Pereira et al. [30
], differences in study design may account for this apparent discrepancy. For example, participants in the study by Pereira et al. [30
] were young, healthy adults who engaged in aerobic activity four times per week; this is contrasted with older adults in our study who were already experiencing cognitive decline and exercised twice per week. This suggests that a higher dose of exercise may result in observable changes in memory more quickly. It is worth mentioning that in our study, the resistance training group also showed a greater reduction in loss after interference after the trial compared with the control group, although this change was not significant. Nevertheless, future studies with larger sample sizes may discover that resistance training does yield similar benefits to aerobic training for verbal memory performance.
Second, we found that both of our experimental exercise groups showed improved reaction time performance for recalling the spatial location of three items, as compared to the balance and tone group. Task performance on the spatial memory test has been shown to systematically decline as a function of load [31
]. That the between-group difference was solely observed for three items—the most difficult condition for the spatial memory task—suggests that exercise distinctively improves higher-level cognitive processing required for more complicated tasks. These findings directly support those from previous studies, where both resistance and aerobic training improved executive functioning—such as selective attention and conflict resolution, as measured by the Stroop task [6
Third, in light of our initial findings regarding improved associative memory performance after six months of twice-weekly resistance training, the results of our present study suggest that different types of exercise may selectively target distinct cognitive processes—and their underlying neural correlates. To recapitulate, we previously reported that resistance training resulted in improved associative memory performance and increased functional activation in three key regions of the cortex: the right lingual and occipital-fusiform gyri and the right frontal pole [11
]. In contrast, here we found that both
types of exercise training led to improved spatial memory. Importantly, spatial memory has neural underpinnings in the hippocampus [21
], thus suggesting that both forms of exercise training may impact hippocampal structure and/or function. Indeed, it has been established that the hippocampus is the structure most sensitive to exercise-induced change via neurogenesis and cell proliferation. For example, aerobic exercise has been found to increase hippocampal volume and levels of BDNF—a neurotrophic factor involved in cell growth and survival and memory promotion [21
]. Thus, while there are multiple potential mechanisms to account for the relationship between cognitive functions and physical activity, such as increased cerebral blood flow [33
], reduced neuroinflammation [34
], and contribution of white matter hyperintensities [35
], we can speculate that underlying changes in hippocampal structure and/or function may be a mediating observed relationship between spatial memory and physical performance.
Finally, the link between physical activity and cognitive functioning is further supported by the significant correlation we have reported between our measure of overall physical performance and spatial memory in the aerobic training group. Notably, these results correspond to our previous findings that improvements in conflict resolution and selective attention, as measured by Stroop performance, were significantly correlated to improved gait speed after 12 months of resistance training [6
]. That these two studies found relationships between different types of exercise (aerobic versus resistance training) and two different measures of cognitive function further supports the notion presented above that the two types of exercise may target distinct molecular pathways [13
]—and thus, modify different subtypes of cognitive function. However, in combination, evidence from these two studies demonstrate that higher levels of physical performance are associated with better cognitive performance. Given that there are multiple ways to improve general physical performance levels, our results therefore suggest that individuals may gain cognitive benefits from a wide variety of exercise options. Future work is needed to explore this possibility.
The conclusions of our study are tempered by our exclusion of men and those older or younger than 70–80 years old. Additionally, our study was only powered to compare the resistance training versus the control group and the aerobic training versus the control group; therefore, we were unable to directly compare changes in performance between our two exercise groups. Hence, future research on how our results may apply to the broader population with larger sample sizes is warranted.
In sum, our study provides preliminary evidence that multiple benefits for memory can be observed after six months of exercise training. However, the mechanisms behind how resistance training and aerobic training may differentially impact cognition remain unclear; thus future work should be aimed at further understanding the contribution of each type of exercise to cognitive functioning, functional plasticity, and brain structure. Furthermore, while our study did find performance improvements after six months, we did not see comparable changes after only three months using a twice-weekly exercise protocol. Therefore, the dose-response relationship of exercise needs to be elucidated so that future recommendations for the most effective program can be translated to health care practitioners and the public.