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.