Interplay of Frailty, Intrinsic Capacity, and Cardiorespiratory Fitness in Older Indian Adults: Insights From a Cross-Sectional Study

Background Frailty, intrinsic capacity (IC), and cardiorespiratory fitness each reflect physiological reserve in aging, yet integrated data combining standardized cardiopulmonary exercise testing (CPET) with the World Health Organization (WHO) Integrated Care for Older People (ICOPE) framework and the Fried phenotype are scarce, particularly in South Asian older adults, where the burden of chronic disease may accelerate functional decline. Methods This cross-sectional study included 130 healthcare-seeking adults aged ≥65 years attending a tertiary geriatric outpatient clinic in India. Frailty was assessed using the Fried phenotype, intrinsic capacity using the World Health Organization Integrated Care for Older People framework across five domains, and cardiorespiratory fitness using CPET to determine maximal oxygen uptake (VO₂max). Associations between IC, frailty, and VO₂max were examined using univariate and multivariable linear regression analyses. Results Frailty prevalence was 73.1% (95/130 participants). Frail participants demonstrated significantly lower skeletal muscle mass, poorer functional performance, and reduced cardiorespiratory fitness compared with non-frail individuals. Higher IC impairment scores were associated with older age, poorer anthropometric measures, reduced physical performance, and lower absolute VO₂max (all p < 0.05). In univariate analyses, several variables, including age, skeletal muscle mass, handgrip strength, gait speed, physical activity, and IC domains, were associated with VO₂max. In a prespecified multivariable regression model adjusting for age, sex, and frailty status, IC total score remained independently associated with lower absolute VO₂max (β ≈ -31 mL/min per point, p ≈ 0.03). Frailty demonstrated a borderline association but did not retain statistical significance after adjustment. Conclusions Impairment of intrinsic capacity was independently associated with lower cardiorespiratory fitness in older adults, independent of age, sex, and frailty status. These cross-sectional findings are hypothesis-generating, and prospective studies are required to determine whether intrinsic capacity precedes decline in aerobic fitness and frailty. Integrating intrinsic capacity assessment with objective measures of aerobic fitness may improve early identification of vulnerable older adults and inform preventive geriatric care strategies.