IJCS | Volume 32, Nº1, January/ February 2019

52 Figure 2 - Double product (DP) in response to high-intensity interval exercise (HIIE) and continuous aerobic exercise (CONT) before and during the first hour following the exercise sessions; * p < 0.05. DP HIIE DP CONT pre Boeno et al. Post-exercise hypotension Int J Cardiovasc Sci. 2019;32(1)48-54 Original Article absolute reduction of 17.9 mmHg and 13.4 mmHg in SBP following HIIE and CONT, respectively. Such decrease is of clinical relevance, with a potential effect on cardiovascular risk reduction. 2 Similar effect has been reported in hypertensive individuals, 20,23,24 with increased resting BP. In this regard, PEH results from a decrease in peripheral vascular resistance by reduction in sympathetic activity. 18,25 In normotensive subjects, PEH seems to be lower than in hypertensive individuals. 7,19 However, in general the protocols of exercise of previous studies had a lowvolume and short duration (20minutes) as compared with the protocol used in our study. Thus, higher volume protocols may be associated with higher sympathetic withdrawal and vasodilation after exercise. In addition, we did not find any significant changes in DBP over time or between the exercise protocols. These findings are in accordance with those reported in the literature, 22 and was somehow expected, since the physiological response of DBP to dynamic exercise is to maintain baseline levels, which were normal in our sample. As expected, myocardial work index, estimated by DP, was significantly higher following HIIE than CONT. This finding is related to the typical elevation in HR in high intensity exercises, with no major clinical impact in this population. In this sense, many strategies involving high intensity exercise and elevatedHR have been shown to promote significant reductions in BP, not only in normotensive but also in hypertensive subjects. 1,16 Besides, PEH at the 15 th minute following HIIE and at the 30 th minute following CONT may be associated with increased DP in the former, leading to increased cardiac output, shear stress and vasodilation induced by nitric oxide. 26 Based on the fact that endothelium-dependent vasodilation in response to exercise seems to be dependent onexercise intensity, 27 thehigh intensityof theHIIEprotocol may be responsible for the earlier PEH in this condition. Among the limitations of this study are the small sample size and the lack of a control condition. Conclusion Both HIIE and CONT, matched by volume, promote PEH of similar magnitude. In HIIE, PEH occurs earlier than CONT, suggesting an additional beneficial effect of this exercise modality on cardiovascular system, in addition to requiring a shorter exercise duration. Further studies using ambulatorial BPmonitoring could provide amore precise understanding of themechanisms of BP behavior in response to HIIE and CONT equalized by volume. Also, studies to investigate the different biochemical andphysiological mechanisms bywhichHIIE and CONT promote PEH are urgently needed. Author contributions Conception and design of the research: Boeno FP, Ramis TR, Farinha JB, Moritz C, Santos VP, Oliveira AR,