The feasibility of implementing high-intensity interval training in cardiac rehabilitation settings: a retrospective analysis

Background Cardiovascular disease is the leading cause of death worldwide. Notwithstanding the well-known benefits of cardiac rehabilitation (CR), adherence to CR remains low, particularly in women. High-intensity interval training (HIIT) has received specific attention as an emerging exercise-training paradigm that addresses frequently cited barriers to CR (i.e. lack of motivation/enjoyment and time, perceiving exercise regime as tiring/boring) and improves cardiovascular risk factors. Previous studies have examined the safety of HIIT in CR; there is little evidence on the feasibility of HIIT in CR. The aims of this study were to evaluate the feasibility of HIIT within a CR setting and examine the sex differences regarding the feasibility of such programming. Methods Patients attended an on-site HIIT CR program (10-min warm-up, 25 min of interspersed high-intensity [HI - 4 min at 85-95% HRpeak] and lower intensity [LO - 3 min at 60-70% HRpeak] intervals, 10-min cool-down) twice weekly for 10 weeks. Heart rate (HR) and the Borg rating of perceived exertion (RPE) scale (6-20 points) were recorded at each session. Feasibility was assessed by: [1] attendance and compliance: the number of sessions attended and the compliance to the prescribed HI and LO HR ranges; [2] the patient experience: patients' perceived effort, program difficulty, if the program was challenging and satisfying; and, [3] safety. Descriptive statistics were used to report the means and their variations. Mann-Whitney U tests and Chi-square analyses were performed to examine sex-differences. Results A total of 151 patients (33% women, 57.5 +/- 9.1 years) attended the HIIT program and completed 16 +/- 5 classes with a low attrition rate (11.3%). Most patients met or exceeded the prescribed target HR for the HI (80%) and LO (84%) intervals, respectively. Patients reported a "somewhat hard" RPE for HI (14 +/- 2 points) and "very light" for LO (10 +/- 2 points) intervals. All patients were satisfied with the program and found it challenging. Most patients found HIIT to be difficult (7 +/- 2 points, scale range 0-10 points), yet safe (97%). Three vasovagal episodes occurred and more women dropped-out of the program than men (p < 0.01). Conclusions HIIT is a feasible, safe and well-received exercise paradigm in a CR setting.