Vascular stiffness, which exemplifies the degradation of the elasticity property of the vessel, is a major hallmark of vascular aging [1]. It has been recognized as a significant clinical predictor of cardiovascular disease (CVD) and mortality [1]. Moreover, it can provide clinically relevant information about CVD beyond the information achieved by traditional CVD risk factors [2]. As such, research and clinical practices have shown growing appeals for measuring vascular stiffness [2, 3, 4].

The current gold standard measure of vascular stiffness is through the carotid-femoral pulse wave velocity (cfPWV) [2, 4]. This method estimates the time transit of pressure waves produced by the myocardial contraction during systole and travels along the arterial tree [5]; faster cfPWV indicates stiffer vessels. Although cfPWV is a noninvasive and safe measure, it has drawbacks. For example, the cfPWV measurement typically requires expensive equipment and extensive training [6], thereby increasing the measurement burden in research and clinical settings. As a result, alternative methods of measuring vascular stiffness are necessary.

Pertinently, recent research has estimated cfPWV (ePWV) by using a mathematical equation that includes age and mean arterial pressure (MAP) [7]. This estimated pulse wave velocity (ePWV) has the same predictive value as cfPWV for CVD, particularly among healthy adults [7]. Subsequent studies have found that ePWV, by itself, can predict atrial fibrillation, CVD mortality, and all-cause mortality [8, 9]. Furthermore, ePWV has significant associations with various measures of vascular aging, including carotid intima-media thickness, carotid elastic modulus, and aortic augmentation index [10]. Yet, ePWV captured different vascular stiffness responses compared to cfPWV in an experimental research setting [11]. Despite this, ePWV remains significant in capturing clinically meaningful vascular stiffness impacts in research and clinical practices, regardless of its parallel responses or correlation with cfPWV.

Of particular interest, robust evidence implies that aerobic exercise can combat increased vascular stiffness. For example, previous systematic reviews and meta-analyses have reported beneficial influences of moderate-intensity continuous training (MICT) on vascular stiffness, measured by cfPWV, in children, adolescents, and adults with different characteristics [12, 13, 14, 15, 16]. Although the positive effects of MICT on cardiovascular health, including cfPWV, manifest [17], adults tend to perform insufficient amounts of MICT [18], with time being frequently self-reported as a constraint [18, 19, 20]. Alternatively, high-intensity interval training (HIIT) has been proposed as an exercise modality that is time efficient [21, 22] and more enjoyable [23] with a comparable or better influence on cardiovascular disease risk factors [24] and vascular stiffness (i.e., cfPWV) [13, 16, 25] compared to MICT in a variety of populations, including overweight and obese adults. Yet, the effects of HIIT and MICT on ePWV have not been explored.

As ePWV is emerging as a valuable cardiovascular measure and HIIT is being recommended for its superiority, it is important to examine the effectiveness of HIIT compared to other exercise modalities on ePWV. Therefore, using data from our previously published randomized controlled trial [21], the purpose of this secondary analysis was (1) to explore and compare the effects of HIIT vs. MICT on ePWV in insufficiently active overweight adults and (2) to explore the superiority effect of HIIT vs. MICT on MAP in insufficiently active overweight adults. It was hypothesized that HIIT would have a superior desirable effect on ePWV and MAP compared to MICT.

Table 2 and Figs. 1,2 compare the effects of the two weeks of HIIT vs. MICT training (8 sessions) on resting ePWV and MAP. The main effects were observed on the resting ePWV and MAP (p 0.05), indicating that both training interventions significantly benefitted these outcomes over time. However, the effect of training intervention and its interaction with time suggests no differences between the effects of HIIT and MICT on ePWV and MAP (p $>$ 0.05 for all).

Fig. 1.

Effects of HIIT (n = 7) vs. MICT (n = 6) on resting estimated pulse wave velocity. HIIT, high-intensity interval training; MICT, moderate-intensity continuous training; M/S, meter per second; ePWV, estimated pulse wave velocity.

Fig. 2.

Effects of HIIT (n = 7) vs. MICT (n = 6) on resting mean arterial pressure. HIIT, high-intensity interval training; MICT, moderate-intensity continuous training; MAP, mean arterial pressure; mmHg, millimeter of mercury.

This unique secondary analysis was performed first to explore the effects of HIIT vs. MICT on ePWV. Further, the superiority of HIIT compared to MICT for improving MAP was evaluated. We revealed novel findings that two weeks of HIIT or MICT resulted in significant and clinically meaningful decreases (favorable effects) in ePWV and MAP in insufficiently active overweight adults. Yet, no interaction effects for a time by the intervention were observed for either outcome, suggesting no superiority of either exercise modality.

Previous studies (n = 10) assessed the influence of HIIT vs. MICT for $\ge$4 weeks on cfPWV in various adult populations. The results of these studies were recently summarized in a systematic review and meta-analysis [25]. Though individual studies observed mixed findings (i.e., favor HIIT, favor MICT, no effects), the pooled estimate showed no significant differences between HIIT and MICT for cfPWV improvements [25]. In harmony with this observation, we detected comparable significant effects of HIIT and MICT on ePWV in overweight adults with no evidence supporting the superiority of HIIT (p-value for the interaction effect $>$0.05). As such, the current evidence suggests the lack of superiority of HIIT compared to MICT for vascular stiffness improvements (i.e., neither cfPWV nor ePWV) following aerobic exercises in adults.

Noteworthy, the difference in ePWV (pre- minus post-intervention) that we observed over time in the HIIT and MICT groups was –0.2 m/s (for both). This ePWV reduction would clinically correlate to 10.6%, 6.2%, and 7% decreases in the risks for hemorrhagic stroke, ischemic stroke, and total stroke, respectively [9]. Furthermore, a reduction of 0.2 m/s in the ePWV would relate to 4.6% and 5.2% reduced risk for all-cause mortality and cardiovascular mortality, respectively [26]. Although, altogether, no superiority by either exercise modality was found, our results indicate that both HIIT and MICT can provide clinically meaningful protective influences on vascular stiffness measured by ePWV in insufficiently active overweight adults.

Subsequently, the influence of HIIT vs. MICT on MAP in adults was also investigated. A recent study reported significant reductions in MAP following six weeks of HIIT (–4.8 mmHg) and MICT (–2.7 mmHg) in insufficiently active men who are overweight or obese [27]; however, no significant interaction effects were noted for the time by which the intervention was observed. In agreement with these findings, we noticed significant decreases in MAP following two weeks of HIIT (–3.7 mmHg) and MICT (–4.5 mmHg) without significant interaction effects in insufficiently active overweight adults. Importantly, these reductions established in MAP (–2.7 to –4.8 in the current and previous studies [27]) would be associated with 2.7% to 4.8% lower risk of major cardiovascular events, including coronary and cerebrovascular events [28]. Thus, although existing evidence indicates no superiority of HIIT vs. MICT for MAP boosting, both exercise modalities can afford clinically desirable influence on MAP.

While the current study did not observe the superior influence of HIIT to MICT on either ePWV or MAP in insufficiently active overweight adults, previous studies reported seemingly contradicting results on several other cardiovascular variables. For instance, an earlier randomized controlled trial found the superior influence of HIIT to MICT on reverse left ventricular remolding, end-diastolic, and end-systolic volume in CVD patients [29]. In contrast, a systematic review and meta-analysis included seven randomized controlled trials that detected no significant differences between the effects of HIIT vs. MICT on either systolic or diastolic blood pressure in patients with pre-to-established hypertension [30]. Although reasons for these discrepancies are not clearly understood, potential explanations may include characteristics of participants (e.g., CVD patients, apparently healthy, overweight/obesity, interindividual variability, hemorheological profile) or exercise protocols (e.g., 2 weeks vs. more than 4 weeks, treadmill vs. cycling) [31, 32]. For example, recent evidence suggests that overweight adults with pre-hypertension exhibit significant differences in BP responses to HIIT compared to normotensive individuals [31]. Hence, there is a need for further well-designed randomized controlled trials that consider important factors such as the prevalence of positive effects on interventions or hemorheological profile to acquire a more comprehensive understanding of the impact of HIIT vs. MICT on cardiovascular health.

Although this study has multiple strengths, such as using a randomized controlled trial design and the gold standard measure of BP assessment, a few limitations should be considered when interpreting our findings. First, both HIIT and MICT interventions lasted for two weeks only. Though this time course was found to significantly boost vascular function [33, 34], a more recent report suggested that vascular adaptation to exercise interventions appeared to peak after eight weeks of exercise interventions [35]. As such, the currently observed improvements in ePWV and MAP may reflect the instant, but not long-lasting, effects of HIIT and MICT. Therefore, future studies comparing the influence of eight weeks of HIIT vs. MICT on ePWV are needed to reach more comprehensive conclusions on the influence of different exercise modalities on ePWV. Furthermore, the sample in the current study was relatively small after a few dropouts (n = 13). This small sample size might have reduced the statistical power, affecting the strength of our findings. Thus, further studies with larger sample sizes are warranted to confirm the currently reported results.

In short, this secondary analysis evaluated the effects of HIIT vs. MICT on ePWV and MPA in insufficiently active overweight adults. We have uniquely revealed that both HIIT and MICT significantly improved ePWV and MAP, with no evidence for the superiority of either exercise modality. Remarkably, these findings suggest that two weeks of HIIT and MICT can provide a clinically meaningful influence on ePWV and MAP, such that the risk of CVD and mortality decreases by large proportions. As such, overweight adults with time constraints for engaging in traditional exercise (i.e., MICT) can accomplish comparable vascular benefits by performing HIIT.

BMI, body mass index; BP, blood pressure; CVD, cardiovascular disease; DBP, diastolic blood pressure; ePWV, estimated pulse wave velocity; HIIT, high-intensity interval training; MAP, mean arterial pressure; MICT, moderate-intensity continuous training; SBP, systolic blood pressure.

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Each author made significant individual contributions to this manuscript. SA, MA, RA, and ABA have given substantial contributions to Conceptualization; SA, MA, AA, RA, HCJ, LS, and ABA have given substantial contributions to methodology; RA and ABA have given substantial contributions to formal analysis; SA, MA, AA, RA, HCJ, LS, and ABA have given substantial contributions to the interpretation of the data; SA, MA, AA, RA, HCJ, LS, and ABA have given substantial contributions to writing—original draft preparation; writing—review and editing. All authors read and approved the final manuscript. All authors have participated sufficiently in the work and agreed to be accountable for all aspects of the work.

This study’s procedure was reviewed and approved by the Institutional Review Board at the University of Louisiana at Monroe (No. 739-2016). All participants voluntarily participated and provided an informed consent form.

The author would like to thank the Researchers Supporting Project Number (RSPD2024R587), King Saud University, Riyadh, Saudi Arabia.

This research received no external funding.

The authors declare no conflict of interest. Lee Stoner is serving as one of the Editorial Board members and Guest Editors of this journal. We declare that Lee Stoner had no involvement in the peer review of this article and has no access to information regarding its peer review. Full responsibility for the editorial process for this article was delegated to Marco Alfonso Perrone, Ferdinando Iellamo and Peter Kokkinos.