1
Introduction
Older adults represented 13% of the total Canadian population in 2005 and will represent an estimated 24% in 2036 . They represented 19% of the total population in France in 2015 and the proportion is still growing . Aging is associated with increased risk of cardiovascular diseases such as coronary heart disease (CHD) . Cardiovascular diseases are among the leading causes of death today in Canada (29%) and in the world (30%) and can lead to $20 billion/year costs in physician services, hospital costs, lost wages and decreased productivity and approximately €196 billion/year in the European Union (€106 billion in healthcare, €44 billion [22%] in informal care, €27 billion [14%] in early mortality and €19 billion in absence from work or early retirement) .
Maximal aerobic power (˙VO2peak)
V ˙ O 2 p e a k
is an independent predictor of mortality and morbidity in CHD patients . Therefore, cardiac rehabilitation programs with an exercise training component such as continuous aerobic exercise training (CAET) were found to be safe and to improve prognosis in CHD patients . The additional clinical benefits of exercise training in CHD patients are well documented and include improvements in cardiovascular, lung and skeletal muscle functions, endurance, quality of life, inflammation, depressive symptoms, stress and cognitive functions . Therefore, exercise training such as CAET is now a cornerstone of the non-pharmacological treatment of patients with CHD and is integrated into the North American and European guidelines .
Recently, a strong clinical interest has emerged in high-intensity interval training (HIIT) in patients with CHD, first mentioned in the American Heart Association recommendations for exercise prescription in 2007 . Actually, HITT is increasingly being mentioned as an exercise modality in the most recent North American and European guidelines for CHD patients .
Here we review different forms of HIIT, their principles and their potential combination with CAET to optimize exercise training adaptations in CHD patients. We discuss only phase II (short-term) and III (long-term/maintenance) exercise training programs with HIIT and CAET separately or combined. Finally, we propose how HIIT with CAET can be integrated into theoretical/practical progressive exercise training models (phase II/III) for CHD patients.
2
CAET for cardiac patients
CAET is still the cornerstone of exercise training programs for CHD patients and is largely recommended worldwide . The program improves prognosis, is safe and feasible and has almost no contra-indications for most patients with stable CHD . CAET programs have shown good short- and long-term clinical benefits, including reduced mortality and/or morbidity , improved V ˙ O 2 p e a k and ventilatory function, relieved clinical symptoms (dyspnea, sleep disorders and depressive symptoms), controlled dyslipidaemia, and reduced endothelial and muscle dysfunction . The main goal of CAET is to perform longer exercise periods in steady-state, which favours oxidative metabolism. For beginners, walking programs remain the most prescribed modality for CHD patients because of the advantages: walking is safe, appropriate for starting exercising, needs no or little supervision and can be performed anywhere (indoor or outdoor). Exercise modalities for CAET include mostly walking, running, cycling, Nordic walking, rowing, swimming, stepping and stairs climbing . In general, CAET leads to higher fat oxidation and longer exercising bouts at intensities from 40% to 50% V ˙ O 2 p e a k for beginners with low physical function/greater cardiac risk (i.e., CHD patients) and 50% to 75% V ˙ O 2 p e a k for CHD patients with higher fitness level or less cardiac risk .
Traditionally, the exercise intensity for CAET is prescribed using percentage maximal heart rate (%HRmax), heart rate reserve (%HRR) and peak power output (%PPO) and patient’s rate of perceived exertion (RPE) (Borg scale: 6–20), with considerable success . The exercise intensity zones for CAET are usually classified as follows (see review for details): light- to moderate-intensity zone (40–50% V ˙ O 2 p e a k , RPE: 11–12) and moderate- to high-intensity zone (50–75% of V ˙ O 2 p e a k , RPE: 12–15). These zones must be mainly considered with phase II (initiation-improvement) and III (maintenance) cardiac rehabilitation (see progression models in Table 1 ). Exercise prescription based on the intensity of the ventilatory threshold, measured during maximal cardiopulmonary exercise test, is also often used for CHD patients, especially those receiving beta-blockers, and corresponds to 50% to 60% V ˙ O 2 p e a k (initial moderate-zone intensity) .
| Patient profile | Stage of training | Prescription (weekly) | CAET | HIIT |
|---|---|---|---|---|
| Low functional status (< 5 METs) | Initiation (week 0–4) | 2–3 × CAET | 50–70% PPO (RPE: 11–15) | Not recommended |
| Improvement (week 4–12) | 2 × CAET and 1 × HIIT (SI) | 50–70% PPO (RPE: 11–15) | HIIT-SI: 15 s to 1 min at 70–100% PPO (RPE: 15–18) | |
| Maintenance (week > 12) | 2 × CAET and 1 × HIIT (SI + MI) | 50–70% PPO (RPE: 11–15) | HIIT-MI: 1–3 min at 90–110% PPO (RPE > 15) HIIT-SI: 15 s to 1 min at 100–120% PPO (RPE: 15–18) | |
| Normal and high functional status (≥ 5 METs) | Initiation (week 0–4) | 2 × CAET and 1 × HIIT (SI) | 50–70% PPO (RPE: 11–15) | HIIT-SI: 15 s to 1 min at 80–100% PPO (RPE: 15–18) |
| Improvement (week 4–12) | 1 × CAET and 2 × HIIT (SI + MI) | 50–70% PPO (RPE: 11–15) | HIIT-MI: 1–3 min at 95–100% V ˙ O 2 p e a k (RPE > 15) HIIT-SI: 10 sec to 1 min at 100–120% V ˙ O 2 p e a k (RPE: 15–18) | |
| Maintenance (week > 12) | 3 × CAET or HIIT (MI + LI) | 50–70% PPO (RPE 14–16) | HIIT-MI: 1–3 min at 95–100% V ˙ O 2 p e a k (RPE > 15) HIIT-LI: 3–4 min at 80–85% V ˙ O 2 p e a k (RPE > 15) |
2
CAET for cardiac patients
CAET is still the cornerstone of exercise training programs for CHD patients and is largely recommended worldwide . The program improves prognosis, is safe and feasible and has almost no contra-indications for most patients with stable CHD . CAET programs have shown good short- and long-term clinical benefits, including reduced mortality and/or morbidity , improved V ˙ O 2 p e a k and ventilatory function, relieved clinical symptoms (dyspnea, sleep disorders and depressive symptoms), controlled dyslipidaemia, and reduced endothelial and muscle dysfunction . The main goal of CAET is to perform longer exercise periods in steady-state, which favours oxidative metabolism. For beginners, walking programs remain the most prescribed modality for CHD patients because of the advantages: walking is safe, appropriate for starting exercising, needs no or little supervision and can be performed anywhere (indoor or outdoor). Exercise modalities for CAET include mostly walking, running, cycling, Nordic walking, rowing, swimming, stepping and stairs climbing . In general, CAET leads to higher fat oxidation and longer exercising bouts at intensities from 40% to 50% V ˙ O 2 p e a k for beginners with low physical function/greater cardiac risk (i.e., CHD patients) and 50% to 75% V ˙ O 2 p e a k for CHD patients with higher fitness level or less cardiac risk .
Traditionally, the exercise intensity for CAET is prescribed using percentage maximal heart rate (%HRmax), heart rate reserve (%HRR) and peak power output (%PPO) and patient’s rate of perceived exertion (RPE) (Borg scale: 6–20), with considerable success . The exercise intensity zones for CAET are usually classified as follows (see review for details): light- to moderate-intensity zone (40–50% V ˙ O 2 p e a k , RPE: 11–12) and moderate- to high-intensity zone (50–75% of V ˙ O 2 p e a k , RPE: 12–15). These zones must be mainly considered with phase II (initiation-improvement) and III (maintenance) cardiac rehabilitation (see progression models in Table 1 ). Exercise prescription based on the intensity of the ventilatory threshold, measured during maximal cardiopulmonary exercise test, is also often used for CHD patients, especially those receiving beta-blockers, and corresponds to 50% to 60% V ˙ O 2 p e a k (initial moderate-zone intensity) .
| Patient profile | Stage of training | Prescription (weekly) | CAET | HIIT |
|---|---|---|---|---|
| Low functional status (< 5 METs) | Initiation (week 0–4) | 2–3 × CAET | 50–70% PPO (RPE: 11–15) | Not recommended |
| Improvement (week 4–12) | 2 × CAET and 1 × HIIT (SI) | 50–70% PPO (RPE: 11–15) | HIIT-SI: 15 s to 1 min at 70–100% PPO (RPE: 15–18) | |
| Maintenance (week > 12) | 2 × CAET and 1 × HIIT (SI + MI) | 50–70% PPO (RPE: 11–15) | HIIT-MI: 1–3 min at 90–110% PPO (RPE > 15) HIIT-SI: 15 s to 1 min at 100–120% PPO (RPE: 15–18) | |
| Normal and high functional status (≥ 5 METs) | Initiation (week 0–4) | 2 × CAET and 1 × HIIT (SI) | 50–70% PPO (RPE: 11–15) | HIIT-SI: 15 s to 1 min at 80–100% PPO (RPE: 15–18) |
| Improvement (week 4–12) | 1 × CAET and 2 × HIIT (SI + MI) | 50–70% PPO (RPE: 11–15) | HIIT-MI: 1–3 min at 95–100% V ˙ O 2 p e a k (RPE > 15) HIIT-SI: 10 sec to 1 min at 100–120% V ˙ O 2 p e a k (RPE: 15–18) | |
| Maintenance (week > 12) | 3 × CAET or HIIT (MI + LI) | 50–70% PPO (RPE 14–16) | HIIT-MI: 1–3 min at 95–100% V ˙ O 2 p e a k (RPE > 15) HIIT-LI: 3–4 min at 80–85% V ˙ O 2 p e a k (RPE > 15) |
3
General principles of HIIT and exercise training implementation for CHD patients
In this section, we review the general principles of HIIT prescription adapted to CHD patients and its place in the context of exercise training implementation. In a second section, we review the available studies comparing HIIT to CAET for CHD patients, an important topic in recent years ( Table 2 ). Finally, we propose a guide for HIIT prescription and implementation combined with CAET for CHD patients ( Table 1 ).
| Author (year) | No. of randomized patients (HIIT/CAET) | Intervention (frequency/duration) | HIIT (intensity/duration) | CAET (intensity/duration) | Cardiovascular AEs (HIIT/CAET) | Other AEs, dropouts/losses and compliance (HIIT/CAET) | Delta of main effects (HIIT vs. CAET) |
|---|---|---|---|---|---|---|---|
| Rognmo et al. (2004) | 11/10 | F: 3 × week D: 10 weeks | I: 4 × 4 min 80–90% V ˙ O 2 p e a k Rec: 3 × 3 min at 50–60% V ˙ O 2 p e a k D: 25 min | I: 50–60% V ˙ O 2 p e a k D: 41 min | 0/0 | 3/1 HIIT: ankle fracture; ack of motivation; ow adherence. CAET: knee injury. Compliance: Compliance of 70% was set as criteria for completing the study, but data not shown | V ˙ O 2 p e a k : 19% vs. 8% No effect on BP |
| Warburton et al. (2005) | 7/7 | F: 2 × week D: 16 weeks | I: 2 min intervals: 85–95% HR/VO 2 reserve Rec: 35–45% HR/VO 2 reserve D: 30 min | I: 65% HR/VO 2 reserve D: 30 min | 0/0 | 0/0 Compliance: HIIT: 98.5% ± 2.0 CAET: 98.8% ± 2.0 | V ˙ O 2 p e a k : 15% vs. 13% c AT: 32% vs. 10% |
| Moholdt et al. (2009) | 33/36 | F: 5 × week D: 4 weeks | I: 4 × 4 min at 90% HRpeak Rec: 3 × 70% HRpeak D: 25 min | I: 70% HRpeak D: 30 min | 0/0 | 4/5 HIIT: 1 leg pain, 1 hip pain, 1 bronchitis and 1 withdrawal CAET: 2 hospitalizations, 1 low adherence, 1 withdrawal and 1 large pericardial effusion. Compliance: data not shown for 4 weeks | V ˙ O 2 p e a k : 12% vs. 7% |
| Moholdt et al. (2012) | 35/72 | F: 3 × week (2 × hospital + 1 × home) D: 12 weeks | I: 4 × 4 min at 85–95% HRpeak Rec: 3 × 70% HR D: 38 min | I: NS D: 35 min | 0/0 | 5/13 HIIT: 1 low adherence, 1 pancreatitis, 1 angina, 1 claudication and 1 gastroenteritis CAET: 7 low adherence, 1 gastrointestinal bleeding, 1 angina, 1 bronchitis, 1 knee surgery, 1 low-back pain and 1 psychiatric disease Compliance d : HIIT: 20.4 ± 5.0 sessions; CAET: 19.1 ± 4.0 sessions | V ˙ O 2 p e a k : 15% vs. 8% |
| Rocco et al. (2012) | 17/20 | F: 3 × week D: 12 weeks | I: 7 × 3 min at RCP Rec: 7 × 3 min at VAT D: 47 min | I: VAT D: 50 min | NS | NS | V ˙ O 2 p e a k : 25% vs. 23% AT 14% vs. 20% |
| Currie et al. (2013) | Total: 23 | F: 2 × week D: 12 weeks | I: 1 min 80–99% of PPO Rec: 1 min at 10%PPO D: 20 min | I: 55–65% of PPO D: 30–50 min | NS | Total: 9 2 data unusable 3 medication changes 4 withdrawal Compliance per 24 sessions: HIIT: 20 ± 3 sessions CAET: 22 ± 2 sessions No difference between groups | V ˙ O 2 p e a k : 20% vs. 22% AT: 22% vs. 23% No effect on BP |
| Keteyian et al. (2014) a | 21/18 | F: 3 × week D: 10 weeks | I: 4 min at 80–90% HRR Rec: 4 × 3 min 60–70% HRR D: 31 min | I: 60–80% HRR D: 30 min | During training: 1 knee pain (HIIT) 1 leg pain (MICET) No events that required hospitalization during or within 3 h after exercise | 6/5 HIIT: 2 lost to follow-up. 2 low-back pain and 2 other medical reasons. CAET: 1 returned to work, 2 lost to follow-up, 1 MI and 1 other medical condition Compliance: HIIT: 71%; CAET: 72% | V ˙ O 2 p e a k : 16% vs. 8% AT: 21% vs. 5% No effect on BP |
| Madssen et al. (2014) | 19/22 | F: 3 × week D: 12 weeks | I: 4 × 4 min at 85–95% HR peak Rec: 3 min at 70% HR peak D: 28 min | I: 60% on HRpeak D: 46 min | HIIT: cerebral hemorrhage | 4/1 HIIT: 2 missing data 1 pneumonia 1 cerebral hemorrhage CAET: 1 withdrawal Total compliance: more than 90% | V ˙ O 2 p e a k : 11% vs. 7% b |
| Kim et al. (2015) | 16/16 | F: 3 × week D: 6 weeks | I: 4 × 4 min at 85–95% HRR Rec: 3 × 3 min 50–70% of HRR D: 25 min | I: 70–85% HRR D: 25 min | 0/0 | 2/2 HIIT: Knee pain Return to work CAET: 2 did not complete the follow-up evaluations Compliance: NS | V ˙ O 2 p e a k : 22% vs. 9% |
| Cardozo et al. (2015) | 24/24 | F: 3 × week D: 16 weeks | I: 2 min at 90% HRpeak Rec: 2 min at 60% HRpeak D: 30 min | I: 70–75% HR peak D: 30 min | 0/0 | 0/0 Compliance: NS | V ˙ O 2 p e a k : 18% vs. 0.5% AT 12% vs. –3% No effect on BP |
| Conraads et al. (2015) | 110/100 | F: 3 × week D: 12 weeks | I: 4 × 90–95% HR peak Rec: 3 × 50–70% HR peak D: 38 min | I: 70–75% HR peak D: 37 min | No AEs during training sessions CAET: 1 AMI, after the last training (PCI was performed). 2 significant ST-depression during the exercise test at 6 weeks (2 PCI performed) | 15/11 HIIT: 3 work, 4 personal reasons, 3 no compliance, 1 disappearance and 4 medical reasons CAET: 3 work, 3 personal reasons, 2 no compliance and 3 medical reasons Compliance: HIIT: 35. ± 1.1 sessions; CAET: 35.6 ± 1.5 sessions; No difference between group | V ˙ O 2 p e a k : 22% vs. 20% No effect on BP |
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