Short Physical Performance Battery (SPPB) assessment is a widely used measure of lower extremity function, strength, and balance. In the Lifestyles Interventions and Independence for Elders (LIFE) Study, baseline SPPB and changes throughout the trial were strongly associated with major mobility disability (MMD). This study further investigated this association by identifying trajectories of SPPB and evaluating the predictive validity of SPPB trajectories for future MMD. Participants (n = 1635) aged 70-89 years were randomized to a physical activity or health education intervention and assessed every 6 months for MMD. We used group-based trajectory models (GBTMs) to identify trajectories of a binary outcome for a decrease from baseline SPPB of ≥1. Multinomial logistic regression explored baseline factors associated with group membership. Survival analyses evaluated the association between trajectories with MMD. The GBTM identified a 3-group model which included a "No Decline" group (46.0%), "Late Decline" group (27.7%), and an "Early Decline" group (26.3%). Adjusting for all other baseline characteristics, group assignment during the previous follow-up visit was strongly associated with MMD at the subsequent period. Comparisons between groups showed a 2-to-3-fold increase in MMD comparing the "Late" to "No" decline group and a 4-to-5-fold increase in MMD comparing the "Early" to "No" decline group. Group membership and impact on MMD was not different between intervention arms. Group-based trajectories of SPPB scores identified distinct subgroups in LIFE Study participants. Using these group assignments in outcome models were highly associated with MMD. GBTMs have potential to identify and improve prediction of aging-related decline to better design and identify patients for interventions.
Keywords: LIFE Study; Short Physical Performance Battery; group-based trajectory models; major mobility disability; physical activity interventions.