Introduction
Mild cognitive impairment (MCI) is characterized by early progressive cognitive decline that lies between normal cognitive decline due to aging and early degeneration of dementia ( Knopman & Petersen, 2014 ; Sachdev et al., 2014 ). MCI is considered a prodromal stage of Alzheimer’s disease (AD), but does not meet the diagnostic criteria for AD ( Jicha et al., 2010 ; Jongsiriyanyong & Limpawattana, 2018 ). Abnormal brain functional activity in MCI is associated with abnormal deposition of amyloid-beta protein, which causes homeostatic imbalance in brain functional network activity by impairing inhibitory gamma-aminobutyric acid (GABA) neurons or increasing synchronization of excitatory synaptic activity ( Mormino et al., 2011 ; Zott & Konnerth, 2023 ). Additionally, an imbalance in the phosphorylation and dephosphorylation of tau proteins in the brain can lead to hyperphosphorylation, forming double-helix filaments and neuronal fiber aggregation, impairing synaptic and neuronal functions, and ultimately affecting cognitive function ( Krance et al., 2019 ).

According to statistics, approximately 15.56% of community members aged 50 years and older worldwide experience MCI ( Bai et al., 2022 ). As the global population ages and life expectancy increases, the incidence of MCI is gradually rising ( Koyanagi et al., 2018 ). MCI is a high-risk group for Alzheimer’s disease, which is currently the fourth leading cause of death in the older adults, after heart disease, tumors, and stroke. It is one of the most significant global public health and social care challenges facing humanity both today and in the future. No single medication can halt or reverse the MCI disease process ( Eshkoor et al., 2015 ). Delayed treatment in the preliminary stages of the illness may lead to worsening of cognitive function, causing a significant burden on individuals, their families, and society ( Petersen et al., 2018 ). Consequently, complementary therapies and non-pharmacological approaches are also gaining attention among researchers, who are gradually shifting their MCI management strategies toward non-pharmacological therapies ( Gauthier et al., 2010 ; Simon, Yokomizo & Bottino, 2012 ).

Exercise is increasingly recognized as a non-pharmacological intervention for MCI ( Teixeira et al., 2012 ; Wang et al., 2020 ). For example, exercise can activate the PI3K/Akt/mTOR signaling pathway to induce autophagy in brain cells, allowing them to reduce the level of amyloid-beta aggregates in the brain through the autophagy system ( Heras-Sandoval et al., 2014 ; Ma et al., 2013 ). Exercise may also protect the hippocampus by preventing neuronal death and limiting the production of inflammatory markers ( Małkiewicz et al., 2019 ). Exercise promotes the formation and survival of new neurons in the hippocampal region, thereby enhancing plasticity and memory function in the hippocampus ( Curlik 2nd & Shors, 2013 ). In recent years, there has been a growing body of clinical research investigating the effects of exercise therapies on cognitive performance in older adults with MCI as well as numerous meta-analyses in this area. Such studies enable the systematic and comprehensive presentation of all available evidence while improving the accuracy of the data by reducing bias from random errors and decreasing random errors generated by individual studies.

Several meta-analyses demonstrated the efficacy of exercise in improving cognitive function in older adults with MCI. However, the quality of these meta-analyses varies widely, and few studies have thoroughly assessed the level of evidence, leaving its certainty largely unclarified. In a related effort, Venegas-Sanabria et al. (2021) conducted an umbrella review to assess the impact of physical activity on cognitive domains in patients with dementia and mild cognitive impairment. Utilizing the AMSTAR2 tool, they evaluated the therapeutic effectiveness of exercise interventions in these populations. Notably, their review targeted two distinct groups and included only 11 studies, a relatively small sample that underscores the challenges in drawing broad conclusions.The primary focus of their research was to explore the efficacy of exercise interventions, rather than scrutinizing the methodological robustness of previous meta-analyses in this area. Evaluating the methodological and certainty of evidence can guide users by synthesizing the findings of meta-analyses at a higher level. This study aimed to reassess the methodological quality and applicability of systematic reviews of exercise therapy in older adults with MCI by assess the meta-analysis literature on the impact of exercise interventions on cognitive function in older adults with MCI using the AMSTAR2 ( Leclercq et al., 2020 ). This assessment seeks to understand the status and existing issues of evidence-based research on the cognitive function of older adults with exercise intervention in MCI and provides a reference for conducting high-quality clinical research on exercise therapy for older adults with MCI to guide clinical decision-making.