Exercise based cardiac rehabilitation (CR) is recognized internationally as a class 1 clinical practice recommendation for patients with select cardiovascular diseases and heart failure with reduced ejection fraction. Over the past decade, several meta-analyses have generated debate regarding the effectiveness of exercise-based CR for reducing all-cause and cardiovascular mortality. A common theme highlighted in these meta-analyses is the heterogeneity and/or lack of detail regarding exercise prescription methodology within CR programs. Currently there is no international consensus on exercise prescription for CR, and exercise intensity recommendations vary considerably between countries from light-moderate intensity to moderate intensity to moderate-vigorous intensity. As cardiorespiratory fitness [peak oxygen uptake (VO₂peak)] is a strong predictor of mortality in patients with coronary heart disease and heart failure, exercise prescription that optimizes improvement in cardiorespiratory fitness and exercise capacity is a critical consideration for the efficacy of CR programming. This review will examine the evidence for prescribing higher-intensity aerobic exercise in CR, including the role of high-intensity interval training. This discussion will highlight the beneficial physiological adaptations to pulmonary, cardiac, vascular, and skeletal muscle systems associated with moderate-vigorous exercise training in patients with coronary heart disease and heart failure. Moreover, this review will propose how varying interval exercise protocols (such as short-duration or long-duration interval training) and exercise progression models may influence central and peripheral physiological adaptations. Importantly, a key focus of this review is to provide clinically-relevant recommendations and strategies to optimize prescription of exercise intensity while maximizing safety in patients attending CR programs.

Purpose: High-intensity interval training (HIIT) is gaining popularity as a training approach for patients attending cardiac rehabilitation (CR). While the literature has focused on the efficacy of HIIT for improving cardiorespiratory fitness (CRF), particularly when compared with moderate intensity exercise, less emphasis has been placed on adherence to HIIT. The aim of this review was to summarize the current literature regarding adherence to HIIT in CR patients with coronary artery disease. Review Methods: A review identified 36 studies investigating HIIT in CR patients with coronary artery disease. Methods and data were extracted for exercise or training adherence (to attendance, intensity, and duration), feasibility of protocols, and CRF. The review summarizes reporting of adherence; adherence to HIIT and comparator/s; the influence of adherence on changes in CRF; and feasibility of HIIT. Summary: Adherence to the attendance of HIIT sessions was high and comparable with moderate-intensity exercise. However, adherence to the intensity and duration of HIIT was variable and underreported, which has implications for determining the treatment effect of the exercise interventions being compared. Furthermore, additional research is needed to investigate the utility of home-based HIIT and long-term adherence to HIIT following supervised programs. This review provides recommendations for researchers in the measurement and reporting of adherence to HIIT and other exercise interventions to facilitate a sufficient and consistent approach for future studies. This article also highlights strategies for clinicians to improve adherence, feasibility, and enjoyment of HIIT for their patients.