According to the WHO Health Statistics Report 2021, the average level of ageing (the ratio of people aged 65 and over to the total population of the region or country) has reached 9.6% worldwide, which means that approximately one in 10 is an older person . The growing prevalence of an ageing population, and with this, the health of older people, is of great concern to the international community. Ageing may bring about both physical frailty and cognitive decline , which can occur together in an older individual. Therefore, what can be done to slow down the process of ageing and its cognitive decline is becoming a major focus of geriatric research.
In 2013, the International Academy of Nutrition and Ageing (IANA) and the International Association of Gerontology (IAGG) first proposed a definition of cognitive frailty (CF): a heterogeneous clinical manifestation characterised by the coexistence of physical frailty and cognitive impairment (Clinical Dementia Scale, CDR = 0.5) . Diagnostic criteria were also specified: at least one of the frailty phenotype diagnoses (reduced body mass, fatigue, sedentary behaviour, slow gait, low muscle strength) was met, CDR = 0.5 and the exclusion of concurrent dementia or other dementias. The consensus was that cognitive frailty is characterised by a reduced cognitive reserve (which refers to the capacity of a given individual to resist cognitive impairment or decline).
In the same year, Woods AJ et al.  suggested that it was unreasonable to exclude patients with brain disorders from the diagnosis of cognitive frailty and concluded that reduced cognitive reserve is not a characteristic manifestation of cognitive frailty. In 2014, Dartigues JF et al.  disputed the issue of cognitive frailty in relation to the body, as well as the distinction between cognitive frailty and other cognitive disorders in the cognitive frailty diagnosis. In 2015, it was suggested that prefrailty should be added to the diagnostic criteria for cognitive frailty and that cognitive frailty should include two subtypes: reversible and potentially reversible . In 2020, Mantovani E et al.  revised the definition of cognitive frailty based on a multidimensional model, whereby the assessment of cognitive frailty should include clinical features, neuropathological changes, biomarkers, disease and medication status.
As research into cognitive frailty continues, more scholars are suggesting [8,9,10,11,12] the use of objective biomarkers as diagnostic indicators to explore the relationship with frailty in terms of structural and functional brain performance. The definition and diagnostic criteria for CF proposed by the IANA/IAGG are widely used in current studies, and although there are differences in the choice of assessment tools for physical and cognitive function, the outcome indicators measured are consistent (i.e., physical function and cognitive function). Future research in CF will require uniform and standardised assessment tools and judgement guidelines adapted to different scenarios.
Studies have shown that the overall prevalence of cognitive frailty in older populations ranges from 0.72% to 50.10% , with 0.72% to 39.70% in Europe and the US and 0.76% to 50.10% in Asian populations. The onset of cognitive frailty can lead to a decline in physical function and mild cognitive impairment, resulting in a reduction in the ability to perform activities of daily living and impaired quality of life, as well as an increased risk of poor health outcomes such as malnutrition, hospitalisation, depression, incapacity, dementia and even death in older people .
However, cognitive frailty is reversible, and physical frailty is a dynamic process . Early-stage screening and reasonable prevention and treatment measures applied in a timely manner can delay the reduction of physiological reserve capacity and reduce the occurrence of adverse health events in older people . In addition, mild cognitive impairment (MCI, cognitive frailty of cognitive impairment mainly refers to mild cognitive impairment) is a transitional state between normal ageing and dementia, and MCI is reversible. It is a critical period in the management of dementia in the elderly . Therefore, cognitive frailty is gaining increasing attention as a new target for healthy ageing  and secondary prevention of dementia .
Many scholars have explored interventions for cognitive frailty. Nonpharmacological interventions are currently the main modalities of cognitive frailty interventions , such as dietary and nutritional guidance interventions, psychosocial support, cognitive training, physical training, physiotherapy programs, etc. Exercise interventions play an important role in nonpharmacological interventions for cognitive frailty, and many scholars have conducted research on exercise interventions for elderly individuals with cognitive frailty, such as resistance exercise, individual progressive dual-task training, multicomponent exercise, and traditional Chinese medicine exercises (Baduanjin, Taijiquan), which are currently emerging. However, there is a large heterogeneity among scholars in the timing, frequency, outcome indicators, and evaluation of the effects of exercise interventions.
The aim of this study was to review the content elements, outcome types and effectiveness of exercise intervention programmes for older people with cognitive frailty, to point out problems with existing exercise intervention programmes and to provide some evidence to inform the implementation and development of future exercise intervention programmes.