Abstract Body (Do not enter title and authors here): Introduction
Cardiometabolic conditions, including heart disease (ischemic heart disease or heart failure; HD) and diabetes mellitus (DM), are associated with accelerated functional decline in older adults. The combined presence of both conditions, cardiometabolic multimorbidity (CMM), may pose compounded risk, yet little is known about how this relationship varies by physical activity (PA), sex, and race/ethnicity.

Objective
To compare two-year functional decline among older adults with CMM, HD-only, DM-only, and controls, and to assess the moderating effect of PA, sex, and race/ethnicity on the association between CMM and physical function in a nationally representative sample.

Methods
We conducted a longitudinal secondary analysis of the 2021-2023 National Health and Aging Trends Study (NHATS, 2021-2023) including 360 community-dwelling older adults. Physical function was assessed using the Short Physical Performance Battery (SPPB). PA was measured via wrist-worn accelerometers and defined as average daily minutes above thresholds for moderate (≥3268 counts/min) and vigorous (≥7890 counts/min) activity. Participants were grouped as HD-only, DM-only, CMM, or neither. Survey-weighted descriptive statistics, linear/logistic regressions, and generalized estimating equation (GEE) tested associations and moderation effects, adjusting for demographic and clinical variables. Analyses were conducted using Stata and R.

Results
At baseline, DM and CMM groups had higher BMI and waist circumference, and included fewer females and more non-white participants than controls. While all groups declined in SPPB and PA over time, the DM group experienced a significantly greater decline than controls. Active participants had significantly higher SPPB scores than non-active participants (β = 1.05, 95% CI [0.64, 1.46], p < .001). However, in the HD group, PA benefits were attenuated. In the DM group, females scored lower than males (interaction β = −1.20, 95% CI [−2.27, −0.14], p = .027), and non-white participants had lower scores than controls (β = −0.73, 95% CI [−1.45, −0.01], p = .046).

Conclusions
Older adults with DM and CMM had worse function and greater decline, especially among non-active individuals, women, and non-white participants. While PA was generally protective, its effects varied by disease group, supporting the need for tailored interventions in cardiometabolic populations.