Cardiovascular effects of high-intensity interval training and moderate-intensity continuous training in sedentary individuals
Date
2018
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
Cardiovascular disease (CVD) continues to be the leading cause of death in the United States. Therefore, identifying and implementing interventions that can help address risk for future CVD continue to be important. Lifestyle modifications are often recommended therapeutic interventions and include weight loss, diet changes, and physical activity. Regular moderate-intensity aerobic exercise has shown to provide positive alterations in cardiorespiratory fitness (CRF), blood pressure (BP), endothelial function, and arterial stiffness. While these benefits exist, a low percentage of the adult population meet the recommendations for regular physical activity, often citing time as a major barrier to adherence. High-intensity interval training (HIIT), which has gained popularity recently, has been suggested as a potential alternative to moderate-intensity continuous training (MCT). The design of HIIT reduces the time commitment necessary by having individuals perform repeated intervals that are high intensity but brief in duration and separated by rest periods. Early evidence has supported the use of HIIT to elicit improvements, similar to MCT, in measures of cardiovascular health in various clinical populations. However, little evidence has been provided for the influence of HIIT on healthy populations. Further investigation is warranted to determine the potential of HIIT as an alternative to MCT for improving cardiovascular health in more than just clinical populations. Therefore, the goal of this study was to determine if HIIT can be an alternative training program to improve BP and measures of cardiovascular health in a healthy but sedentary population. The central hypothesis is that despite a shorter exercise duration, HIIT will improve resting BP, vascular function, and BP reactivity similar to MCT. ☐ Twenty healthy, sedentary individuals (15 females and 5 males) between the ages of 20-44 years completed this study. After pre-training testing, participants were randomized into two groups, MCT (29.3 ± 2.4 years, n=11) and HIIT (29.4 ± 1.8 years, n=9). Both training programs included training sessions 3x per week and were 8 weeks in length. The MCT group performed 30 minutes of continuous exercise at 65-70% maximum heart rate (HRmax) while the HIIT group performed 10 x 60 second intervals at 90-95% HRmax with each repetition being followed by a 60 second active rest interval. All sessions were supervised and performed on an upright stationary cycle ergometer. Outcomes were assessed pre- and post-training. ☐ The goal of Aim I was to assess CRF, resting and ambulatory BPs, and BP reactivity. A maximal graded exercise test (GXT) on a cycle ergometer was utilized to assess CRF. Resistance started at 50 watts and increased 25 watts every 2 minutes until exhaustion. Resting peripheral BPs were assessed in the seated position after 10 minutes of quiet rest using an oscillometric BP device. Participants wore an ambulatory BP monitor (ABPM) for 24-hours to assess peripheral and central BPs. Central BP measurements were assessed in the supine position via pulse wave analysis using radial tonometry. Additionally, peak BP response during the GXT was assessed. Beat-to-beat BPs were evaluated during handgrip exercise (40% maximal voluntary contraction), post-exercise ischemia (PEI), and the cold pressor test (CPT). The goal of Aim II was to assess vascular function. Conduit artery function was assessed via brachial artery flow mediated dilation (FMD). Lower leg vascular function was evaluated by assessing the blood flow response to passive limb movement (PLM). Finally, carotid-femoral and femoral-distal pulse wave velocity (PWV) was assessed to evaluate central and peripheral arterial stiffness, respectively. ☐ Training compliance was 96% for both the MCT and HIIT groups. Both training programs resulted in significant increases in total exercise time (MCT: 727 ± 65 vs. 789 ± 66 seconds and HIIT: 659 ± 84 vs. 752 ± 77 seconds, p<0.05) and maximal oxygen consumption (VO2max) (MCT: 27.31 ± 2.54 vs. 28.71 ± 2.68 ml/kg/min and HIIT: 27.04 ± 3.15 vs. 30.60 ± 2.35 ml/kg/min, p<0.05). The primary outcome of the study was resting peripheral BP and significant decreases in systolic blood pressure (SBP) were observed for the MCT (119 ± 2 vs. 115 ± 3 mmHg, p<0.05) and HIIT (112 ± 4 vs. 105 ± 3 mmHg, p<0.05) groups post-training. A significant decrease in mean arterial pressure (MAP) was observed but only in the MCT (88 ± 2 vs. 85 ± 2 mmHg, p<0.05) group. Neither training program altered 24- hour ambulatory BP measures or measures of resting central BP. There was also no effect of either training program on peak SBP response during the GXT. During handgrip exercise, significant interactions (p<0.05) were observed for SBP, diastolic blood pressure (DBP), and MAP changes from baseline. Post hoc analysis revealed significantly smaller increases in BP from baseline post-training in the MCT group for DBP and MAP (p<0.05), while a trend appeared for SBP (p=0.062). No significant differences were observed within the HIIT group. Significant interactions were also demonstrated for BP changes from baseline during PEI (p<0.05). Significantly larger increases in SBP, DBP, and MAP (p<0.05) from baseline were revealed post-training only in the HIIT group after post hoc analysis. During the CPT, a significantly larger increase in BP from baseline was observed for the HIIT group in SBP, DBP, and MAP post-training (p<0.05) but no changes in MCT were seen. Following training, neither training program elicited improvements in FMD, carotid-femoral PWV, or femoraldistal PWV (p<0.05). However, a significant effect of time was observed for the peak blood flow response to PLM. Post hoc analysis did not reveal any individual group differences in MCT or HIIT (p>0.05). Interestingly, no other measures of PLMinduced hyperemia demonstrated significant improvement following training. ☐ In conclusion, these data provide evidence that 8 weeks of HIIT can result in positive improvements in CRF and resting peripheral BP measurements that are similar to those observed following 8 weeks of MCT. HIIT appears to be an effective alternative to MCT for improving CRF and resting peripheral BP in a generally healthy, sedentary population. Additionally, it appears that exercise augments the peak blood flow response to PLM but not other measures of PLM-induced hyperemia. Finally, HIIT also resulted in augmentation of the BP response from baseline during PEI and CPT compared to MCT which requires further study.