"Brain-muscle loop" in the fragility of older persons: from pathophysiology to new organizing models

The imperative action of the geriatric medicine is to prevent disability in older persons. Many epidemiological studies have been conducted in the last decades for improving knowledge of the aging process and their interactions with age-related diseases, especially for the identification of the relationship between sarcopenia and loss of mobility. Factors influencing muscle integrity can be classified into six main physiologic subsystems, but the central nervous system certainly plays a crucial role for maintaining muscle integrity in older persons. Recent data show that the reduced muscle strength and not muscle mass could be considered the core of the fragility in predicting changes of gait velocity and mobility and conferring a higher risk of mortality in older persons. Sarcopenia and cognitive decline could, therefore, produce slow gait velocity in older persons, with devastating effect and consequences. Perhaps the most notorious corollary is falling, which is often caused by an underlying gait problem. Injuries caused by accidental falls range from relatively innocent bruises to major fractures or head trauma. Another important consequence is reduced mobility, which leads to loss of independence. This immobility is often compounded by a fear of falling, which further immobilises patients and affects their quality of life and physical performance.

When we search the association between brain pathology and muscle function in older persons, we amazingly find that established composite measure of physical frailty is associated with brain pathology. Sarcopenia, which produces muscle dysfunction, slow gait velocity and cognitive decline, could share a strong bidirectional relationship, and this suggests the coexistence of both cognitive and motor dysfunctions in older persons to characterize a new syndrome characterized by slow gait and cognitive complaints, the motoric-cognitive risk syndrome (MRC).

In this review, we want to emphasize the relationship between memory complaints with muscle function integrating cognitive and physical evaluation, even with amyloid PET study, to identify older patients at high risk of cognitive and physical decline.