The Determination of Step Frequency in 3-min Incremental Step-in-Place Tests for Predicting Maximal Oxygen Uptake from Heart Rate Response in Taiwanese Adults

The maximal oxygen uptake (VO 2max ) prediction models established by step tests are often used for evaluating cardiorespiratory fitness (CRF). However, it is unclear which type of stepping frequency sequence is more suitable for the public to assess the CRF. Therefore, the main purpose of this study was to test the effectiveness of two 3-min incremental step-in-place (3MISP) tests (i.e., 3MISP 30s and 3MISP 60s ) with the same total number of steps but different step-frequency sequences in predicting VO 2max . In this cross-sectional study, a total of 200 healthy adults in Taiwan completed 3MISP 30s and 3MISP 60s tests, as well as cardiopulmonary exercise testing. The 3MISP 30s and 3MISP 60s models were established through multiple stepwise regression analysis by gender, age, percent body fat, and 3MISP-heart rate. The statistical analysis included Pearson’s correlations, the standard errors of estimate, the predicted residual error sum of squares, and the Bland–Altman plot to compare the measured VO 2max values and those estimated. The results of the study showed that the exercise intensity of the 3MISP 30s test was higher than that of the 3MISP 60s test (% heart rate reserve (HRR) during 3MISP 30s vs. %HRR during 3MISP 60s = 81.00% vs. 76.81%, p < 0.001). Both the 3MISP 30s model and the 3MISP 60s model explained 64.4% of VO 2max , and the standard errors of the estimates were 4.2043 and 4.2090 mL·kg −1 ·min −1 , respectively. The cross-validation results also indicated that the measured VO 2max values and those predicted by the 3MISP 30s and 3MISP 60s models were highly correlated (3MISP 30s model: r = 0.804, 3MISP 60s model: r = 0.807, both p < 0.001). There was no significant difference between the measured VO 2max values and those predicted by the 3MISP 30s and 3MISP 60s models in the testing group ( p > 0.05). The results of the study showed that when the 3MISP 60s test was used, the exercise intensity was significantly reduced, but the predictive effectiveness of VO 2max did not change. We concluded that the 3MISP 60s test was physiologically less stressful than the 3MISP 30s test, and it could be a better choice for CRF evaluation.