OBJECTIVE: To obtain clinical usefulness of knee extension- flexion exercise by comparing the exercise indexes between treadmill exercise and knee extension-flexion exercise and to collect reference of exercise indexes using knee extension-flexion exercise. METHOD: Sixty four young healthy subjects participated in two modes of exercise. Subjects performed exercise using isokinetic dynamometer in one leg knee extension-flexion exercise and treadmill running using Bruce protocol in treadmill exercise. We recorded oxygen consumption, heart rate during rest and exercise. RESULTS: When comparing exercise indexes using treadmill exercise, we obtained relative exercise indexes using knee extension-flexion exercise, male 15.96%, female 15.77% in work rate, male 48.46%, female 52.53% in peak oxygen consumption, male 73.57%, female 80.82% in peak heart rate, male 65.97%, female 65.20% in oxygen pulse, male 56.07%, female 62.50% in peak tidal volume, male 82.56%, female 82.53% in peak respiratory rate, male 47.79%, female 49.48% in peak minute ventilation. In dynamic variables, we obtained male 266.82%, female 292.98% in ratio increase in oxygen consumption to increase in work rate. CONCLUSION: Knee extension-flexion exercise showed enough response to evaluate cardiorespiratory function through low work rate. Therefore knee extension-flexion exercise may be used for an exercise tolerance test in patients who cannot perform established exercise tolerance test.