IJCS | Volume 32, Nº4, July/August 2019

378 Figure 2 - Validity testing of the first and second evaluations of ventilatory thresholds and maximal oxygen uptake. The first and third columns of the graphs show scatter plots and correlation coefficients. The diagonal lines represent the identity lines. Graphs on the second and fourth columns are Bland-Altman plots. The horizontal lines represent upper limit, bias and lower limit for difference between the two evaluations. CPET: cardiopulmonary exercise test. Belli et al. Speed and grade increment during cardiopulmonary Int J Cardiovasc Sci. 2019;32(4):374-383 Original Article 183; 195] vs 183 ± 7 [95% CI = 178; 188], p < 0.01) (Figure 3B). The responses were also significantly different when HR was analyzed as a percentage of the peak (Intensity: p < 0.01; Protocol: p < 0.01; Interaction: p = 0.01). The submaximal exercise sessions were analyzed from 10 to 40 min, corresponding to the steady-state phase of exercise (Figure 4). Similarly to the comparison of protocols, subjects exhibited stable HR responses (Figure 4A), with higher levels observed during the session based on the speed protocol. Blood lactate concentrations (Figure 4B) were stable after 20 min, with higher concentrations observed during the speed protocol. To maintain a stable HR, speed was progressively reduced (Figure 4C), resulting in a reduction of VO 2 (Figure 4D). VE/VO 2 increased progressively (Figure 4E), but there were no significant differences between protocols. The respiratory exchange ratio decreased progressively (Figure 4F), with significant differences between the protocols. Perceived rates of respiratory (Figure 4G) and leg (Figure 4H) exertion were significantly higher during the sessions based on the speed protocol. Discussion The major finding of the present study was that a treadmill protocol based mainly on speed increments resulted in higher VO 2 and HR corresponding to the VT 1 and VT 2 when compared to a treadmill protocol based mainly on grade increments. Moreover, the choice of the protocol had a significant impact on exercise prescription based on ventilatory thresholds. To our knowledge, this is the first report describing the impact of the type of increment during CPET performed on the treadmill on aerobic exercise prescriptions. Previous studies have shown that, when the cycle ergometer is used for the detection of ventilatory