Effects of physical activity on delayed memory measures in randomized controlled trials with nonclinical older, mild cognitive impairment, and dementia participants

ABSTRACT

Introduction: Longitudinal studies have found that physical activity protects against Alzheimer disease, but the mechanism is unknown. The prevailing model derives from animal research and has physical activity directly affecting brain physiology by increasing brain volume, brain-derived neurotrophic factor (BDNF), and hippocampal neurogenesis with consequent gains in neuropsychological test scores. Supporting evidence has been mixed, with physical-activity-related gains across multiple neuropsychological domains considered indicative of the protective effect. Hippocampal-mediated delayed memory functioning is the first neurocognitive skill to be impaired in the early stages of Alzheimer disease, and physical-activity-related gains on delayed memory measures would provide the strongest support for the model. Results: Review of 26 randomized controlled trials with nonclinical older, mild cognitive impairment, and dementia participants found only one with significant physical-activity-related gains in delayed memory compared to controls. This evidence does not support the physiological brain change model. Similarly, there is questionable support from those randomized controlled trials that have measured physical-activity-related brain volume and blood BDNF levels (neurogenesis having no valid labeling technique in living humans). Conclusion: Physical-activity-related protective effects against Alzheimer disease are likely mediated through pathways outside the central nervous system.

KEYWORDS:

• Aerobic exercise
• brain-derived neurotrophic factor
• hippocampal volume
• neurogenesis
• neuropsychological testing

Disclosure statement

No potential conflict of interest was reported by the author.

Additional information

Funding

No funding has been received for this study and/or preparation of this manuscript.