【PURPOSE】 The present study was conducted to develop a formula for estimating the maximum oxygen intake, which was obtained from heart rate (HR) walking efficiency, with a final goal of establishing a simple method for measuring physical endurance.【METHODS】 Thirty healthy males (19 to 38 years old) were ordered to walk on a treadmill at four different speeds (33.3, 66.6, 100, and 133.3 m/min) for 3 minutes each, and at a speed of 133.3 m/min with a 5% incline for another 3 minutes, for 15 minutes total. HR walking efficiency was calculated from the HR and oxygen intake during walking, and the speed efficiency curve was obtained. From this curve, the maximum efficiency value, width of curve, and the optimal speed were then obtained.【RESULTS】 The maximum oxygen intake indicated significant correlations with the maximum efficiency value, width of curve, and optical speed. Multiple correlation analysis revealed the following formula for estimating the maximum oxygen intake; maximum oxygen intake = 0.5917 × width of curve - 0.7460023 × optimal speed- 0.69805 × age + 0.39778 × body height - 58.50948 (R=0.87173,p<0.0001).【CONCLUSION】These results indicate tha