Determining reduced functional capacity in older adults using research-grade wearable accelerometers: a secondary analysis of the study of muscle, mobility, and aging.

Background: Reduced functional capacity (FC) is associated with adverse surgical outcomes in older adults. Current FC assessments rely on questionnaires; however, it remains unclear whether accelerometer-measured daily activity provides a more accurate evaluation. Our primary aim was to identify accelerometer-based variables associated with reduced FC. Methods: We conducted a secondary analysis of the Study of Muscle, Mobility and Aging (SOMMA) cohort. Participants were community-dwelling adults (non-surgical) aged ≥70 yr and recruited between the years 2019 to 2021 at the University of Pittsburgh (Pittsburgh, PA, USA) and Wake Forest University School of Medicine (Winston-Salem, NC, USA). Participants were included if they completed cardiopulmonary exercise testing and had valid wear time (≥3 days) for two accelerometers used in the SOMMA study (ActiGraph GT9X and activPAL4). We applied classification and regression tree and random forest models to accelerometry-derived metrics. For comparison, we constructed a logistic regression model using modified Duke Activity Status Index 4-Question (M-DASI-4Q) scores extrapolated from the Community Healthy Activities Model Program for Seniors questionnaire. Results: The final cohort included 640 participants (57.2% [366/640] women; mean age 76.3 [5.0] yr), of whom 18% (114/640) had reduced FC (peak oxygen uptake [VO2peak] <16 ml kg-1 min-1). Participants with adequate FC had higher daily step counts (5843.9 [2950.4] vs 2988.3 [1757.2] steps per day; P<0.001) and more time in moderate-to-vigorous physical activity (118.0 [62.2] vs 59.9 [42.4] min day-1; P<0.001) compared with those with reduced FC. The accelerometer-based random forest model (AUC 0.79) did not significantly outperform the M-DASI-4Q model (AUC 0.72; P=0.16). Conclusion: Among community-dwelling older adults, daily step count and time in moderate-to-vigorous activity were most associated with FC, but the accelerometer-based model showed only fair discrimination to identify participants with reduced FC. Validation in surgical populations is needed.