IJCS | Volume 32, Nº4, July/August 2019

379 Table 1 - Ergometric data, cardiorespiratory, and metabolic results at rest and incremental exercise test with the speed and grade protocol Speed (n = 9) M ± SD (95% CI) Grade (n = 9) M ± SD (95% CI) Rest Heart rate (beats.min -1 ) 72 ± 12 (65; 79) 73 ± 12 (66; 81) Blood lactate (mmol.L -1 ) 1.79 ± 0.62 (1.41; 2.17) 1.69 ± 0.59 (1.33; 2.06) Peak exercise Time (s) 694 ± 206 (574; 821) 568 ± 151 (483; 662)* Speed (km.h -1 ) 13.5 ± 2.5 (12.0; 14.9) 6.2 ± 0.3 (6.0; 6.4)* Grade (%) 2.6 ± 2.6 (1.2; 4.3) 19.7 ± 4.9 (16.8; 22.7)* Heart rate (beats.min -1 ) 189 ± 6 (184; 193) 183 ± 7 (179; 187)* Oxygen uptake (ml.kg -1 .min -1 ) 35.8 ± 10.8 (29.7; 43.2) 34.7 ± 9.7 (28.9; 41.0) Carbon dioxide output (L.min -1 ) 2.69 ± 1.0 (2.05; 3.28) 2.88 ± 1.16 (2.16; 3.54) Minute ventilation (L.min -1 ) 102 ± 33 (81; 122) 106 ± 34 (84; 127) Respiratory exchange ratio 1.14 ± 0.11 (1.06; 1.20) 1.25 ± 0.11 (1.17; 1.31) Perceived exertion Respiratory 9 ± 2 (8; 10) 9 ± 1 (8-; 10) Legs 8 ± 2 (7; 10) 9 ± 1 (9; 10)* Maximal blood lactate during recovery Blood lactate (mmol.L -1 ) 9.07 ± 2.29 (7.30; 10.83) 9.95 ± 2.25 (8.21; 11.68) Time to maximal (min) 2 ± 2 (0.5; 3) 3 ± 2 (1; 5) M: mean; SD: standard deviation; 95%CI: 95% confidence interval. * p < 0.01. Belli et al. Speed and grade increment during cardiopulmonary Int J Cardiovasc Sci. 2019;32(4):374-383 Original Article thresholds, the results are independent of the rate of increment in power output. 9,31,32 The detection of VT 1 is also not affected by the rate of increment in exercise intensity on the treadmill. 14 Despite the fact that the treadmill is the ergometer of choice in many clinical settings, no study has previously evaluated the impact of changing grade versus speed on the detection of ventilatory thresholds using the treadmill. Kinderman et al., 15 evaluated the influence of different incremental treadmill protocols on the detection of the 4 mmol.L -1 lactate threshold. In agreement with what had been shown for the cycle ergometer, 9 when fixed, absolute blood lactate concentrations are used to detect thresholds, and the results were dependent on the protocol used. In the present study, VO 2 values at the ventilatory thresholds were ~7% higher on the speed- based protocol when compared to the grade-based protocol. Likewise, HR at the ventilatory thresholds was ~8% higher on the speed-based protocol when compared to the grade-based protocol. The mechanisms by which a speed-based protocol results in higher ventilatory thresholds when compared to a grade-based protocol are not readily apparent from our data. Based on the findings of Kelsey & Duffin, 19 in which greater ventilatory responses to speed than grade increments were observed on the treadmill for the same VO 2 , one would expect lower ventilatory thresholds with the speed protocol, assuming that greater limb movement frequency would be responsible for our findings. An additional potential explanation for the lower ventilatory thresholds for the grade-based protocol is activation of a larger muscle mass with increments in grade. 23 During uphill (+10%) running, the volume of activated limb muscles increases from 67% to 73%,