###### Abstract  
The purpose of this study was to compare the validity of three submaximal exercise tests (SMETs) and develop practical predictive models for the VO2 max in Korean adults. A total of 541 (287 males and 254 females) adults participated in this study. Their ages ranged from 19 to 64. The VO2 max was measured using the maximal-graded exercise treadmill test. The SMETs were performed by a treadmill test, the YMCA step test, and the PACER test. Regression analysis was conducted to compare the validity of the VO2 max predictive equations using SMETs. The validity of the predictive models was evaluated using explanatory power, standard error of estimate (SEE), and Bland-Altman analysis. The explanatory power between the measured VO2 max and the predicted VO2 max was 58.0% (<0.001), 59.2% (<0.001), and 71.7% (<0.001), respectively. The SEEs were 4.545, 4.478, and 3.732 (mL/kg/min). The models were significant predictors of VO2 max and had acceptable validity in a large sample of Korean adults. Especially, among the predictive models, PACER had the highest acceptable effectiveness. Therefore, the equations developed in this study are recommended to better evaluate the cardiovascular endurance of Korean adults. cardiovascular endurance; VO2 max; step test; treadmill test; PACER; 20 m multistage shuttle run test; prediction model +
Footnote †: journal: Medical  
linear relationship with oxygen intake. Typical submaximal exercise tests include the step test [10], the treadmill test [11], and the 20-m shuttle run test [12]. The step test is a widely used submaximal exercise test because it is simple and does not occupy a lot of space. The step test repeats ascending and descending stairs and cardiovascular endurance is evaluated mainly by the heart rate during the recovery period after performing for a certain period of time [13]. In the step test, there are several tests depending upon the height and speed of the stairs [14]. This is because the results may vary depending upon race and physical characteristics such as sex, age, height, and weight [15; 16], so an estimation formula should be developed considering these characteristics. The treadmill test, which estimates the maximal oxygen intake using a treadmill without measuring the actual maximal intake, can be placed in various spaces such as laboratories and fitness centers. The test is easy to manage and exercise intensity can be controlled according to speed and inclination, so it measures and evaluates cardiovascular endurance. Most previous studies that estimated the VO2 max using a treadmill developed an estimation formula that included speed and heart rate as major explanatory variables during walking or running on a treadmill [17; 18]. The progressive aerobic cardiovascular endurance run (PACER) 20-m multistage shuttle run test, which is performed by running a distance of 20 m back and forth, can estimate VO2 max using only the individual's physical information and the number of round trips without measuring heart rate [19; 20]. In addition, multiple people can be measured at the same time, and the occurrence of safety accidents can be minimized because it is not boring, and participants automatically drop out according to ability [21]. Therefore, a formula for estimating the VO2 max using the PACER test has been developed through several previous studies. [PERSON] and [PERSON] first developed an estimation equation using the PACER test in 1988 and showed a high correlation (0.84) with the maximal exercise test [19]. Unlike the maximal exercise test, these submaximal exercise tests are a relatively safe method for estimating exercise capacity using exercise intensity, heart rate, and the physiological response up to the point when the subject is comfortable exercising [22]. However, the accuracy of cardiovascular endurance evaluation is poor [23; 24]. Therefore, it is important to use an appropriate submaximal exercise test method to accurately measure the VO2 max and the efficient test time [25; 26].