Background: Physical capacity (PC) defines the limits for physical activity (PA), while activities in daily life typically remain submaximal. Older adults whose daily activities approach their physical capacity may experience less functional decline, though prospective evidence is limited. This study compared changes in physical function over a four-year follow-up between community-dwelling older adults categorized based on their combined baseline physical capacity and physical activity.

Methods: 312 community-dwelling older adults (75-85 years, 60% women) participated in this study. Baseline physical capacity was measured using the 5-second Mean Amplitude Deviation (MAD) during a maximal 10-meter walking test. Physical activity was assessed based on individuals' ~99.25th percentile MAD values from free-living accelerometry (representing an intensity equivalent to 75 min/week of physical activity), which were then used for group categorization into lowPC-lowPA, lowPC-highPA, highPC-lowPA, and highPC-highPA profiles. Physical function was assessed with the Short Physical Performance Battery (SPPB) and the 5x Sit-To-Stand (5xSTS) test. Analyses used nonparametric tests and generalized estimating equations.

Results: Significant changes in SPPB and 5xSTS were observed in all profiles (p < 0.05) except for the lowPC-highPA profile. The decline in SPPB was greater for low versus high physical activity profiles in both PC profiles (high PC: B -0.61, SE 0.24, 95% CI -1.08, -0.15; low PC: B -0.96, SE 0.35, 95% CI -1.62, -0.32), but no significant difference was found for the decline in 5xSTS time between physical activity profiles in either physical capacity profile.

Conclusions: Engaging in physically demanding activities, irrespective of baseline physical capacity, may help slow functional decline in old age. Older adults should be encouraged to engage in physically demanding activities to enhance their functional capacity.