Increased arterial stiffness is a strong and independent predictor of cardiovascular and all-cause mortality in patients with coronary artery disease (CAD).1 Moderate-to-vigorous intensity continuous exercise training (MICT) has been shown to improve arterial stiffness in such patients.2 Yet, the role of different exercise modalities and intensities on arterial stiffness in patients with CAD has not been elucidated. We recently demonstrated greater improvements in functional capacity, quality of life, and depression severity following Nordic walking (NW) than high-intensity interval training (HIIT) and MICT in patients with CAD.3,4 No previous trial has compared the efficacy of these exercise paradigms in improving arterial stiffness. Nordic walking, which simultaneously engages the upper and lower body, may confer superior vascular health (eg, increasing pulsatile flow) benefits when compared with other exercise modalities and intensities. Further, alternatives to traditional MICT, such as NW and HIIT, may increase adherence to exercise programs in these patients. The purpose of this substudy was to compare the effects of 12 wk of NW, HIIT, and MICT on arterial stiffness in patients with CAD.
METHODS
This sub-study presents secondary data analyses from the larger CRX randomized controlled trial (http://ClinicalTrials.gov #NCT02765568) at the University of Ottawa Heart Institute (UOHI). The eligibility criteria have been previously published.3 In brief, participants included those: (1) with CAD who recently underwent a percutaneous coronary intervention or coronary artery bypass graft surgery within the previous 18 wk, (2) referred to a cardiovascular rehabilitation (CR) program at the UOHI, (3) willing to attend an on-site CR program 2 d/wk for 12 wk, and (4) 40-74 yr of age. All patients provided written informed consent (REB #20160127-01H).
Patients with CAD were randomly assigned to: (1) NW (walking with NW poles: resting heart rate [HR] + 20-40 bpm), (2) HIIT (aerobic exercise equipment and dance/movement-based routines: 4 x 4-min of high-intensity work periods at 85-95% peak HR interspersed with 3-min low-intensity work periods at 60-70% peak HR), or (3) MICT (walking and aerobic exercise equipment: resting HR + 20-40 bpm) 2d/wk for 12 wk.3 The volume and intensity of exercise for the three groups has been described in detail previously.3 Briefly, each HIIT session was 45 min in duration and the NW and MICT sessions were 60 min in duration. At baseline and within 1 wk of completing the 12 wk intervention, aortic stiffness was measured by cardiac output, stroke volume (SV), augmentation index (AIx) with and without normalization for an HR of 75 bpm (AIx@75), augmentation pressure, total vascular resistance, and pulse wave velocity (PWV) using the Mobil-O-Graph device (IEM Gmbh). Vascular measures were taken after 10 min of rest in a seated position. Linear mixed-effects models with repeated measures were used to compare groups over time using SPSS for Windows (IBM Corp), and P < .05 was considered significant.
RESULTS
A total of 130 patients with CAD (aged 61 +/- 7 yr; males: 85%) were randomized to NW (n = 43), HIIT (n = 43), or MICT (n = 44). Participant characteristics were previously described.3 The Table shows that significant main effects of time were observed for SV ([DELTA] = 5.485 m/L, F = 8.530, P = .004), with a time x group interaction (F = 3.710, P = .027) revealing a greater improvement in SV following NW compared with HIIT (F = 5.748, P = .01) and MICT (F = 5.494, P = .022). A significant time x group interaction (F = 3.700, P = .028) was observed in AIx@75, showing a greater reduction following NW than MICT (F = 7.388, P = .008). No significant differences were observed in any other arterial stiffness parameters. The HIIT sessions demonstrated higher HR and ratings of perceived exertion compared with the MICT and NW sessions. Sex-specific analyses were performed, and no significant differences were found; however, this sub-study may have been underpowered for such analyses.
DISCUSSION
Patients with CAD present higher arterial stiffness when compared with the general population. This can lead to a reduction of coronary perfusion pressure and increased left ventricular afterload, promoting left ventricular remodeling and dysfunction.5
We found that 12 wk of NW was superior in improving SV and AIx@75 compared with HIIT and MICT, respectively. Similarly, a previous trial comparing 12 wk of NW and MICT demonstrated greater improvements in SV ([DELTA] = 21.0 vs 17.0 mL, P < .001, respectively) in patients with acute coronary syndrome,6 but not in AIx following 4 mo of NW in individuals with type 2 diabetes.7 Interestingly, NW compared to traditional walking led to a sustained (ie, 3-6 mo) reduction in carotid to radial PWV in overweight and obese post-menopausal women.8 We did not observe any differences in PWV. Nordic walking and the resistance required to properly use the poles demand a greater muscle activation (ie, 70-90% of the upper body's skeletal musculature), energy expenditure (ie, 8% metabolic equivalent of task [METs]), and cardiorespiratory fitness (ie, oxygen uptake [VO2] 11-23%) compared with other traditional aerobic movement-based exercise.9 For instance, similar or higher values of VO2 and HR have been observed when comparing NW and jogging at the same speed.9 The combination of the mechanisms mentioned previously has shown to reduce oxidative stress (eg, normalize shear stress through nitric oxide mediated vasodilation) and vascular inflammation (eg, reduction in advanced glycation end product accumulation, inhibition of smooth muscle cell proliferation), which may explain the superior benefits on arterial stiffness parameters following NW than HIIT and MICT. There were differences in exercise volume and intensity between groups. The greater improvements of NW suggest potential benefits of higher exercise volume, as also previously observed with the 6-min walk test.3 Yet, the MICT group did not similarly improve, suggesting the NW poles may play a role in the exercise stimulus.
Previous studies have compared HIIT and MICT and did not observe any significant differences in arterial stiffness in adults of any health status10 or patients with CAD.11 However, Taylor et al11 showed that a 4 wk center-based HIIT program was superior to MICT in improving endothelial function in patients with cardiovascular disease. Although endothelial dysfunction and arterial stiffness present pathophysiologic differences, they have common underlying mechanisms (ie, oxidative stress, inflammation markers), which may be linked.2 Exercising at high intensities, therefore, has shown to increase blood flow and shear stress stimulus, promoting greater vascular adaptation when compared with MICT, which we, surprisingly, did not observe in our trial.
These results highlight that NW is an appropriate alternative to HIIT and MICT for improving specific arterial stiffness parameters in individuals who have recently undergone coronary revascularization. Our findings are novel and help to provide direction for future randomized controlled trials (eg, multicentered, equal sex representation) to confirm these results.
Acknowledgments
This study was funded by the Innovations Fund of the Alternate Funding Plan for the Academic Health Sciences Centres of the Ministry of Ontario (J. Reed, A. Pipe) and the Heart and Stroke Foundation of Canada (B. Reid).
REFERENCES