Background The physiological mechanisms underlying reduced exercise performance in older adults are poorly understood. Maladaptation’s of skeletal muscle oxidative function with age have been implicated but are difficult to measure non-invasively during exercise. Therefore, reliably measuring muscle oxidative capacity alongside traditional markers of cardiorespiratory fitness is an important step towards better understanding exercise physiology with age. Method Participants (n=96; 72=male, mean age=71.5±6.3years) undertook a 6-minute stepper test. Oxygenated(HbO2) and deoxygenated haemoglobin(Hb) were monitored in the calf muscle using near infrared spectroscopy(NIRS) and peak muscle oxygen consumption(muscleVO2) was measured as the slope of the difference between these signals during arterial occlusion immediately post-exercise. Transient occlusions allowed a time constant of muscleVO2 recovery to be generated. Adipose tissue thickness (ATT) at the NIRS measurement site was assessed by 2D ultrasound (Vivid I, GE) and peak total body VO2 was measured using breath-by-breath gas analysis(K4B2, CosMed, Rome). A sub-set of participants repeated the test. Data are means±SD of differences; reproducibility was assessed using concordance correlation coefficient (ccc), 95% CI. Linear relationships were compared using β-coefficients from the regression model. Results Peak muscleVO2 and recovery time constants were reproducible, mean differences were 0.82±0.9µM/s (ccc=0.73,CI= 0.5, 0.96) and 18.8±53.4s (ccc=0.64, CI=0.34, 0.95), respectively. After adjustment for total body VO2 and exercise performance (steps completed), thicker adipose tissue predicted lower peak muscleVO2 (standardised β-coefficient= 0.44, CI= p<0.01) but did not influence the time constant (standardised β-coefficient=0.04). The time constant for muscleVO2 recovery predicted exercise performance independently from total body peak VO2(standardised β-coefficient= -0.17, p=0.01). Conclusions Local peak muscle VO2 and its recovery time constant can be measured reproducibly in older adults but when comparing peak muscleVO2 between individuals, ATT should be accounted for. After adjustment for cardiorespiratory fitness (peak total body VO2), peak muscleVO2 independently predicted performance suggesting impaired skeletal muscle oxidative capacity is an important mechanism underlying reduced exercise performance in older adults.