The association between motor capacity and mobility performance: Frailty as a moderator

Background: In older adults, the linkage between laboratory-assessed 'motor capacity' and 'mobility performance' during daily routine is controversial. Understanding factors moderating this relationship could help developing more valid assessment as well as intervention approaches. We investigated whether the association between capacity and performance becomes evident with transition into frailty, that is, whether frailty status moderates their association. Methods: We conducted a cross-sectional analysis of the observational (blinded for review) study in a community-dwelling cohort in (blinded for review). Participants were N = 112 older adults aged 65 years or older who were categorized as non-frail (n = 40), pre-frail (n = 53) or frail (n = 19) based on the Fried frailty index. Motor capacity was quantified as normal (NWS) and fast walking speed (FWS). Mobility performance was quantified as 1) cumulated physical activity (PA) time and 2) everyday walking performance (average steps per walking bout; maximal number of steps in one walking bout), measured by a motion sensor over a 48 h period. Hierarchical linear regression analyses were performed to evaluate moderation effects. Results: Unlike in non-frail persons, the relationship between motor capacity and mobility performance was evident in pre-frail and frail persons, confirming our hypothesis. A moderating effect of frailty status was found for 1) the relationship between both NWS and FWS and maximal number of steps in one bout and 2) NWS and the average steps per bout. No moderation was found for the association between NWS and FWS with cumulated PA. Conclusion: In pre-frail and frail persons, motor capacity is associated with everyday walking performance, indicating that functional capacity seems to better represent mobility performance in this impaired population. The limited relationship found in non-frail persons suggests that other factors account for their mobility performance. Our findings may help to inform tailored assessment approaches and interventions taking into consideration a person's frailty status.