Background Functional capacity declines with age leading to disability and increased cost of health and social care.(1) In older adults, factors that influence the ability to sustain sub-maximal exercise (a marker of functional capacity) are not well defined. We aimed to determine the contribution of cardiac function, peripheral desaturation, oxygen extraction and skeletal muscle oxidative capacity to sub-maximal exercise performance in a population-based sample of older adults. Methods Participants were older adults (>60 years old) enrolled in the Southall And Brent REvisited (SABRE) study.(2) Sub-maximal exercise performance was assessed as the highest achieved whole-body oxygen uptake (VO2) during a 6-minute stepper test (6MST). Near Infrared Spectroscopy (NIRS) was used to assess local skeletal muscle oxygen extraction and desaturation at the start and end of exercise and maximum oxidative capacity. Echocardiography was used to measure resting cardiac output (CO) and CO during exercise was estimated by multiplying resting stroke volume by exercise heart rate. Analysis was by multiple linear regression adjusted for confounders: age, sex, ethnicity, diabetes and obesity. Results 363 participants (71.3±6.4 years old, male; n=212) undertook the 6MST, skeletal muscle desaturation measurements and echocardiography. Skeletal muscle desaturation and cardiac output were independently associated with whole-body VO2 (standardized β adjusted for confounders: 0.27, p<0.001 & 0.30, p<0.001, respectively). Local skeletal muscle oxygen extraction was independently associated with whole-body VO2 (standardized β adjusted for confounders & cardiac output: 0.37, p<0.001). Maximum oxidative capacity was not associated with VO2 (β: 0.01, p=0.4). Conclusion Local oxygen extraction and desaturation in skeletal muscle are independent predictors of self-selected exercise performance in older adults. These associations persist with adjustment for cardiac output suggesting local capacity to extract oxygen could be a major limiting factor for self-paced exercise in older adults.