Exercise rehabilitation programs have been recognised as non-pharmacological therapies for reducing cardiovascular morbidity and mortality. Several types of training protocols are currently used in rehabilitation, but there is still debate regarding the intensity and type of exercise training that can provide optimal effects . High Intensity Interval exercise (HIIT) has gained popularity the last years, even in patients with chronic diseases; however, the exact mechanisms offering haemodynamic benefit have not been totally clarified.
A recent article in the European Journal of Preventive Cardiology , attempted to address this. Specifically, Vesterbekkmo et al., evaluated the progression of coronary atheromatic plaques volume in 60 patients with stable coronary artery disease following percutaneous coronary intervention, after initiation of a 6 month-HIIT program. Using intravascular ultrasound, the researchers illustrated the anti-atherogenic effects of intensive exercise, revealing a significant increase in VO2 max in cardiorespiratory exercise larger atheroma volume regression in the HIIT group compared with usual care. Beneficial effects were observed in body weight management, but not in LDL cholesterol and Apo-B levels, that could explain atherosclerosis regression.
The authors conclude that there is increasing evidence that alternations in local haemodynamic forces in the coronary tree are pivotal for the dynamic biology of atheroma progression and regression, implicating endothelial function. A higher amount of shear stress, which facilitates positive physiologic adaptations in the vasculature, seems to be induced by HIIT compared to other forms of mild intensity exercise. Even in patients with heart failure, HIIT seems do induce larger benefits in peak VO2 and VE/VCO2 . The beneficial effect of intermittent exercise may be due to a greater generation of large shear stress forces within the endothelium leading to improvement in endothelial function, increasing muscle mass, hence improving oxygen metabolism, diastolic function, left ventricular work and ventriculoarterial coupling.
Although this study faces some limitations due to the small sample size, the exercise levels obtained in the intervention group may be hard to obtain without ongoing and continuous supervision, as the authors indicate. In addition, there is inadequate representation of women (only 21%), as well as lack of older patients with less engagement in physical activity and with more diffuse atherosclerotic disease. However, the reported findings deserve further attention. In previous studies comparing moderate intensity continuous exercise with HIIT, cardiorespiratory response, as expressed with VO2 max was greater with interval training than with continuous training. Moreover, interval training was associated with reverse left ventricular remodeling, expressed with a significant decrease in diastolic and systolic left ventricular volume with a parallel increase in left ventricular ejection fraction. which was not observed in the continuous training or control groups .
The question that remains to be answered is which type of exercise program would benefit our patients most? A recent review article  showed that arterial stiffness increases with age in healthy women and has an inverse relationship with exercise intensity. A total of fifty-one papers were included in this study, showing improvements in arterial stiffness observed following an 8-week high-intensity aerobic programme in young women: hypoxic high-intensity interval training in middle-aged women and moderate intensity aerobic programme in older women. It seems that when prescribing an exercise program, one should consider, among other clinical factors, age and physical status of the individual.