# The feasibility of implementing high-intensity interval training in cardiac rehabilitation settings: a retrospective analysis PMID: 32612840 Journal: BMC Sports Science, Medicine and Rehabilitation Published: 2020-06-29 Authors: Way KL, Vidal-Almela S, Keast ML, Hans H, Pipe AL, Reed JL ## Question Is supervised HIIT feasible, acceptable, and safe in a real-world cardiac rehabilitation setting, and are there sex differences in feasibility outcomes? ## Summary In a retrospective analysis of 151 cardiac rehabilitation patients, a supervised 10-week group HIIT program using 4 x 4-min intervals was generally feasible and well received. Participants attended 16 +/- 5 of 20 classes, 73% attended at least 70% of classes, most met or exceeded HR targets, all questionnaire respondents were satisfied and found the program challenging, and 97% reported it felt safe. Three vasovagal episodes occurred and no delayed adverse events were reported. ## Population - 151 cardiac rehabilitation patients with CVD or CVD risk factors; 50 women and 101 men. - Sample size: 151 - Age: 57.4 +/- 9.5 years overall - Sex: 50 women, 101 men; 67% men - Fitness level: Baseline exercise level >=4 METS and able to sustain at least 30 min aerobic exercise - Health status: Cardiac rehabilitation population with CVD or risk factors; 75% coronary artery disease, 59% PCI, 17% CABG, many on cardiovascular medications ## Methodology - Retrospective mixed-methods feasibility analysis of a clinical cardiac rehabilitation program - 10 weeks - On-site cardiac rehabilitation program at the University of Ottawa Heart Institute ## Protocol - Modified Norwegian cardiac rehabilitation HIIT. - Modality: Aerobic equipment or dance/movement-based HIIT. - Work intervals: 4 min high-intensity interval. - Recovery: 3 min lower-intensity interval. - Sets or repetitions: 4 x 4-min HI intervals. - Intensity: 85-95% HRpeak for HI and 60-70% HRpeak for LO. - Session duration: 45 min including 10-min warm-up, 25-min interval block, and 10-min cool-down with resistance/stretching. - Frequency: 2 sessions/week. - Program length: 10 weeks. - Progression: Initial 2-week familiarization; HRpeak from graded exercise test when available or Gellish equation with beta-blocker adjustment. ## Outcomes ### Attendance and attrition Status: improved Attendance was high and attrition was low overall, though women dropped out more often than men. 16 +/- 5 of 20 classes attended; 73% attended >=70%; dropouts 17/151 (11%); women 20% vs men 7%, p=0.034 ### Intensity compliance Status: mixed Most participants met or exceeded HR targets, but many reported RPE below encouraged target ranges. HI HR: 53% complied and 27% exceeded; LO HR: 42% complied and 42% exceeded; 58% below HI RPE target and 61% below LO RPE target ### Patient experience Status: improved Questionnaire respondents perceived HIIT as difficult/challenging but satisfying and confidence-building. RPE HI 14 +/- 2; RPE LO 10 +/- 2; difficulty 7 +/- 2; 100% challenging, 100% satisfied, 97% safe among respondents with available data ### Safety Status: mixed Three vasovagal episodes occurred, no delayed adverse events were reported, and most respondents perceived the program as safe. 3 events out of 2224 training sessions; no delayed adverse events; 97% reported safe ## Practical Insights - In cardiac rehabilitation, HIIT feasibility depends on medical screening, HR monitoring, staff supervision, and accessible location. - RPE alone may under-detect whether cardiac patients are reaching intended HR zones. - A gradual post-interval intensity reduction may be important after high-intensity cardiac rehab intervals. ## Limitations - Retrospective single-center clinical program analysis. - No comparator group. - HR data were self-reported/recorded rather than downloaded from monitors. - No data on compliance to exact interval durations. - Feedback questionnaire data were available only in a subset. - Male-predominant sample; sex comparisons should be interpreted cautiously. ## Safety And Adherence - Three vasovagal episodes occurred early in the program; a step-by-step reduction in exercise intensity after high-intensity work bouts was implemented and no further vasovagal syncope was reported. No delayed adverse events were reported. ## Original Sources - [PubMed](https://pubmed.ncbi.nlm.nih.gov/32612840/) (pubmed) - [DOI](https://doi.org/10.1186/s13102-020-00186-9) (doi) - [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7325048/) (full text) ## Agent Guidance Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.