The cerebral changes induced by exercise interventions in people with mild cognitive impairment and Alzheimer's disease: A systematic review

Objectives: This study aimed to summarize the effects of exercise on the brain structure and function measured by imaging and electroencephalography methods in people with mild cognitive impairment and Alzheimer's disease. Methods: We systematically searched different electronic databases, including PubMed, Web of Science, Embase, Cochrane Central Register of controlled trials, SPORTDiscus, PsycINFO up to September 2021. Randomized controlled trials with exercise interventions in people with mild cognitive impairment and Alzheimer's disease were included. The outcomes included all the structural and functional brain changes measured by neuroimaging and electroencephalography approaches. All the outcomes were summarized and tabulated. The protocol has been registered on the PROSPERO (CDR42020192579). Results: Nineteen articles from 12 trials were included. Most studies focused on people with mild cognitive impairment and revealed positive effects on the volumes of hippocampus and cingulate cortex, the resting state functional connectivity between the hippocampus and other brain regions, the brain activity in several regions, the cerebral blood flow, electroencephalogram, and P300 latency and amplitude. Different types of exercise could produce distinct effects and intensity was a factor affecting the effects of aerobic and resistance exercise interventions. Meanwhile, limited studies paid attention to people with Alzheimer's disease and showed insignificant results. Conclusions: Exercise has positive effects on the brain structures and functions in people with mild cognitive impairment, while for people with Alzheimer's disease, limited studies revealed insignificant effects.