Mild cognitive impairment has a direct effect on gait speed even when accounting for frailty

Background: Gait—a frequently performed activity of daily living—is thought to reflect multiple dimensions of an individual’s physical and cognitive status. Individuals with frailty or mild cognitive impairment (MCI) show decreased gait speed. However, previous studies have not simultaneously considered both statuses, although they frequently co-occur and may act as confounders. The direct association between frailty and gait is well-understood. In contrast, the association between cognitive decline—independent of physical function—and decreased gait speed, as well as the relationship among these three factors (frailty, cognitive decline, and gait speed), is not fully understood. Methods: This study examined the effect of MCI on gait speed after accounting for frailty. Older individuals were categorized as (1) frailty with MCI, (2) frailty without MCI, (3) pre-frailty with MCI, (4) pre-frailty without MCI, (5) non-frailty with MCI, and (6) non-frailty without MCI. Frailty was assessed using the Kihon checklist and MCI using the Montreal Cognitive Assessment. Participants completed a 10-m walk test under two conditions: comfortable walking and fast walking. Two types of analyses were conducted: mediation analysis and two-way analysis of covariance (ANCOVA). Results: Mediation analysis supported independent relationships between frailty and MCI status and gait speed, suggesting a direct association between MCI and gait speed, even when accounting for frailty. In addition, two-way analysis of covariance indicated significant main effects of both frailty and MCI on gait speed, with no significant interaction between them under the two walking conditions. Conclusions: These findings suggest that the observed association between MCI and gait speed is largely independent from frailty status, providing additional evidence supporting the association between cognitive function and gait performance.