J.-S. Kim, J.-S. Oh, and S.-G. Kim, “The correlation analysis between the estimation of VO₂max using the Harvard step test, Queens’ college step test, 90-90 Queens’ college step test, and the measured VO₂max value from Cardiopulmonary Exercise Testing (CPX)”, JRTDD, vol. 6, no. 10s(2), pp. 1617–1621, Dec. 2023.