Commonly used measures of physical activity (PA) fail to account for heterogeneity in maximal capacity between individuals. Utilizing the concept of heart rate reserve, we estimated minute level physical exertion (PE) among BLSA subjects with at least 3 days of Actiheart data (n = 411). Subjects’ average time spent in each of sedentary, light, moderate and vigorous PE was associated with age adjusting for demographics, chronic conditions, and PA. Despite a significant decline in total PA with age (p < 0.001), time spent in moderate and vigorous PE is positively associated with age in both women (pmoderate < 0.001, pvigorous < 0.001) and men (pmoderate = 0.137, pvigorous = 0.222). Chronic conditions are also generally associated with increased average PE. Our results suggest that individuals with decreased capacity are, on average, engaging moderate and high relative intensity activities at a rate comparable to, or higher than, that of healthier individuals.