Validity of a perceptually-regulated step test protocol for assessing cardiorespiratory fitness in healthy adults

To determine whether maximal oxygen uptake (VO₂max) could be predicted accurately and reliably from a 2-step, perceptually-regulated exercise test (PRET) in healthy adults.

Sixteen participants (31.7 ± 11.3 years, 3 females) completed three PRETs (separated by 24-72 h) and one maximal, perceptually-regulated, graded exercise test (PRETmax) on a motorized treadmill. Oxygen uptake (VO₂) and heart rate (HR) were recorded during each test. VO₂ values for RPE range 9-15 were extrapolated to RPE 20 and age-predicted maximal HR (HRmax) using individual linear regression analysis to predict VO₂max values compared to measured VO₂max.

VO₂ and HR values were consistent between each of four RPE levels of the PRET. ICC values ranged between 0.76 and 0.85. Predicted VO₂max from both methods were lower than measured VO₂max (p < 0.01). Limits of agreement (LoA) for measured (41.4 ± 5.3 ml kg^-1 min^-1) versus predicted VO₂max from each of the three PRETs using RPE20 were -1.2 ± 15.6, -1.0 ± 7.2 and -2.1 ± 5.5 and for HRmax were -1.8 ± 4.2; -2.6 ± 4.2 and -2.4 ± 4.4 ml kg^-1 min^-1 for PRET 1, 2 and 3, respectively.

The step PRET elicited significant and reliable increases in VO₂ across the four RPE levels, but under-estimated treadmill VO₂max. However, there was better agreement between measured and predicted VO₂max when extrapolated to HRmax. As evidence indicates the underestimation of VO₂max is explained by the difference in the mode of exercise, the step PRET provides a simple and convenient test of cardiorespiratory fitness.