IJCS | Volume 32, Nº4, July/August 2019

382 Belli et al. Speed and grade increment during cardiopulmonary Int J Cardiovasc Sci. 2019;32(4):374-383 Original Article adjusted according to the HR corresponding to the mean point between VT 1 and VT 2 . Our data show that the choice of protocol has a significant impact on the exercise intensity prescribed for aerobic training based on the determination of ventilatory thresholds. The speed-based protocol resulted in a higher HR, blood lactate, speed, and perceived exertion during the exercise sessions. The size of this difference (~8% for HR and ~2 mmol.L -1 for blood lactate) is substantial. If, for instance, the exercise prescription were to be set at the HR corresponding to VT 2 , the steady state blood lactate concentration would be reached using a grade-based protocol, but blood lactate would likely accumulate if a speed-based protocol was used. 13 Our study has several limitations. Ventilatory thresholds were visually determined by one experienced investigator (JPR) blinded to the identity of the subjects and the utilized protocol. Despite the fact that we did not evaluate the inter-observer agreement for the detection of thresholds, the intra-observer agreement was appropriate, 11,27 as demonstrated by similar mean values, high correlation coefficients, and Bland-Altman analyses within acceptable limits. Moreover, the standard criteria used in clinical practice, including ventilatory equivalents, V-slope, and the end-tidal CO 2 , were applied. 3,36 With this approach, the reproducibility for the detection of the ventilatory threshold was in agreement with previous studies. 31,36-38 Furthermore, to avoid the walking-running transition, which affects the linearity of VO 2 response, both protocols began at 5.5 km/h, a speed at which all subjects were jogging. Perhaps, other faster transition speeds might produce different results, which in fact may be the subject of a future experiment. Therefore, our findings cannot be extrapolated to protocols in which individuals do not run. Finally, our findings are limited to healthy young adults, and therefore may not be applicable to elderly individuals, children or those with pathological conditions. Conclusion A speed-based protocol results in higher ventilatory thresholds when compared to a grade-based protocol during CPET performed on a treadmill. These findings have a significant impact on cardiorespiratory and metabolic responses to prescribed exercise intensity in healthy subjects. Due to fact that exercise prescription based on CPET often requires a high degree of confidence and safety, it is necessary to keep in mind that the same protocol must be utilized when the subject is re-tested during clinical practice. Finally, the speed-based protocol was more convenient because it was more applicable for exercise prescription. Acknowledgements This work was supported by the Hospital de Clínicas de Porto Alegre Fund for the Incentive of Research (FIPE/ HCPA) from Porto Alegre, Brazil; the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Brasília, Brazil; and the Brazilian Research Council (CNPq) Brasília, Brazil. Author contributions Conception and design of the research: Belli KC. Acquisition of data: Belli KC, Silva PF. Analysis and interpretation of the data: Belli KC, Silva PF, Franzoni LT, Myers J, Stein R. Statistical analysis: Belli KC, Franzoni LT. Writing of the manuscript: Belli KC, Myers J, Stein R. Critical revision of themanuscript for intellectual content: Belli KC, Franzoni LT, Myers J, Stein R. Potential Conflict of Interest No potential conflict of interest relevant to this article was reported. Sources of Funding There were no external funding sources for this study. Study Association This article is part of the thesis of doctoral submitted by Karlyse C. Belli, from Universidade Federal do Rio Grande do Sul . Ethics approval and consent to participate This article does not contain any studies with human participants or animals performed by any of the authors.