IJCS | Volume 32, Nº4, July/August 2019

375 Belli et al. Speed and grade increment during cardiopulmonary Int J Cardiovasc Sci. 2019;32(4):374-383 Original Article exercise prescription among both athletes and patients with cardiovascular disease. 4-7 Tests based on ramp protocols are recommended for CPET because they generally provide a linear increase in VO 2 relative to workload, particularly when performed on the cycle ergometer. 8-11 The VT 1 and the VT 2 occur at similar VO 2 , independent of the rate of increase in exercise intensity on the cycle ergometer 12,13 and the same is true for the determination of the VT 1 on the treadmill. 14 Regardless of differences between cardiorespiratory fitness measured on a cycle ergometer and a treadmill, the choice of the ergometer may influence VT 1 determination. 14,15 In the Americas, the treadmill is the exercise mode of choice in clinical settings. 1,2,16 When using the treadmill, it can be difficult to achieve a linear response in metabolic rate because of the walk-run transition, 17 the rate of increase in speed and grade, 18-20 or handrail support and its effect on economy. 14 Moreover, there is little information available on the effects of different treadmill ramp protocol increments on the detection of the VT 1 and VT 2 . 14,15 Changes in speed and/or grade may be used to develop an appropriate treadmill ramp protocol in efforts to make the work rate increments as linear as possible. 20 In this regard, work rate increments can have notable effects on the response to exercise due to the disproportionate interaction between muscle activation, 21-23 kinematic variables related to gait, and oxygen uptake (VO 2 ) kinetics; 24 and each of these factors can significantly influence VO 2 during exercise. Moreover, the impact of the type of increment during CPET performed on a treadmill with regard to exercise prescription has not been previously studied. Therefore, this study was conducted to compare the effects of two treadmill ramp protocols on the detection of VT 1 and VT 2 . We applied one protocol mainly using speed increments and another using mainly grade increments. In addition, we evaluated the steady-state response to exercise prescription based on the measured ventilatory thresholds from the two protocols. Material and methods Participants Four male and five female subjects, aged 29 ± 6 years [95% CI = 25; 33], height 170 ± 8 cm [95% CI = 165; 175], and weight 65 ± 8 kg [95% CI = 60; 71], participated in the study. All subjects were active and otherwise healthy as determined by medical history, physical examination, and resting and exercise electrocardiograms. None were taking medications. The subjects did not vary their activity levels during the testing period. All rights and privileges were honored in accordance with an established human subject’s protocol, and informed consent was obtained. The ethics committee of the institution approved the protocol. Protocol The protocol included two maximal incremental CPETs and two submaximal exercise sessions, performed on different days; the type of increment was chosen in random order. All tests were performed in a comfortable laboratory environment, with a minimum of 48 hours between tests. The CPET system underwent gas and volume calibration before each exercise test. No handrail support was allowedduring the tests. 3 The randomization of protocols was performed by an independent researcher using the software Rx 64 version 13. The protocol randomized for the first incremental CPET was the same for the first submaximal exercise session. Incremental cardiopulmonary exercise tests Two incremental protocolswereused fordetermination of VT 1 , VT 2 , andVO 2 max. The subjects were positioned on the treadmill (Inbramed, TK10200, Porto Alegre, Brazil) and initially walked 2.0 km.h -1 and 1% grade for 2 min. The speed protocol then increased to 5.5 km.h -1 and 1% of grade and increments of 0.1 to 0.3 km.h -1 were added every 15s (Figure 1A), with a constant grade (Figure 1C). If the maximal speed of the treadmill (16 km/h) was attained, exercise intensity was further increased by grade increments of 0.5% per 30s. The grade protocol started at 5.5 km.h -1 and 1% of grade, with increments of 0.1 km.h -1 every 45s (Figure 1B) and 1% increases in grade every 30s (Figure 1D). Subjects exercised until volitional fatigue. During recovery from the incremental tests, subjects walked on the treadmill at 2 km.h -1 for 7 min. Fingertip blood samples were collected at 1, 3, 5, and 7 min for the determination of maximal blood lactate during recovery. Cardiorespiratory variables Heart Rate (HR) was determinate based on the R-R intervals from a twelve-lead electrocardiogram