It is unknown if vigorous to maximal aerobic interval training (INT) is more effective than traditionally prescribed moderate-intensity continuous aerobic training (MCT) for improving peak oxygen uptake (V o 2 ) and the left ventricular ejection fraction (LVEF) in patients with heart failure with reduced ejection fraction. MEDLINE, PubMed, Scopus, and the Web of Science were searched using the following keywords: “heart failure,” high-intensity interval exercise,” “high-intensity interval training,” “aerobic interval training,” and “high-intensity aerobic interval training.” Seven randomized trials were identified comparing the effects of INT and MCT on peak V o 2 , 5 of which measured the LVEF at rest. The trials included clinically stable patients with heart failure with reduced ejection fraction with impaired left ventricular systolic function (mean LVEF 32%) who were relatively young (mean age 61 years) and predominantly men (82%). Weighted mean differences were calculated using a random-effects model. INT led to significantly higher increases in peak V o 2 compared with MCT (INT vs MCT, weighted mean difference 2.14 ml O 2 /kg/min, 95% confidence interval 0.66 to 3.63). Comparison of the effects of INT and MCT on the LVEF at rest was inconclusive (INT vs MCT, weighted mean difference 3.29%, 95% confidence interval −0.7% to 7.28%). In conclusion, in clinically stable patients with heart failure with reduced ejection fraction, INT is more effective than MCT for improving peak V o 2 but not the LVEF at rest.
Randomized controlled exercise intervention trials for clinically stable patients with heart failure with reduced ejection fraction (HFREF) have primarily incorporated moderate-intensity continuous aerobic exercise training (MCT). Despite beneficial antiremodeling benefits, MCT is associated with a small (0.6 ml/kg/min) to moderate (3 ml/kg/min) increase in peak exercise oxygen uptake (V o 2 ). We recently reported that a single bout of near maximal (96% of peak heart rate) aerobic interval exercise increased postexercise regional and global left ventricular (LV) systolic function in clinically stable patients with HFREF. However, it is unclear if vigorous to maximal aerobic interval training (INT), based on American College of Sports Medicine guidelines for the classification of exercise intensity, is more effective than traditional MCT at improving peak V o 2 and the LV ejection fraction (LVEF) in patients with HFREF (mean LVEF ≤50%). Accordingly, we performed a systematic review and meta-analysis to examine the effects of INT compared with those of MCT on these outcomes.
Methods
We searched MEDLINE (1948 to 2012), PubMed, Scopus (1960 to 2012), and the Web of Science (no limit to years published) using the following keywords: “heart failure,” high-intensity interval exercise,” “high-intensity interval training,” “aerobic interval training,” and “high-intensity aerobic interval training.” We also hand-searched the reference lists of all identified studies and previous reviews. The primary and secondary end points were peak V o 2 and the LVEF at rest, respectively. Two investigators independently reviewed the titles and abstracts of all citations. Data were extracted by 2 reviewers (M.J.H., M.M.) and analyzed using the change from baseline data, and results were combined as weighted mean differences with 95% confidence intervals using RevMan software (Cochrane Collaboration, Copenhagen, Denmark). Heterogeneity was assessed using chi-square tests. Quality assessment of randomized controlled trials and concealment of treatment allocation were determined as previously described.
Results
After initial review of 88 citations and 5 additional citations identified from manual searches ( Figure 1 ), 7 unique randomized trials were identified comparing the effects of INT with those of MCT on peak V o 2 in patients with HFREF, 5 of which measured the LVEF at rest ( Table 1 ). Reasons for exclusion are reported in Figure 1 . The trials included clinically stable patients with HFREF with impaired LV systolic function (mean LVEF 32%) who were relatively young (mean age 61 ± 9 years) and predominantly men (82%). No trial was double-blind (as expected with this type of intervention), very few trials described randomization procedures, no trial reported blinding of assessors across all objective outcomes, and concealment of treatment allocation was unclear for all trials. Thus, trials scored relatively poorly on the Jaded scale ( Table 1 ).
| Study | Group (n) | Cause of HF (DCM/ICM) (%) | Age (yrs) | Men | LVEF (%) | Training Program | Jaded Score (1–5) | ||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Mode | Frequency (Days/Week) | Intensity | Duration (Minutes) | Program Length (Weeks) | |||||||
| Dimopoulos et al | MCT (14) | 57/36 | 62 | 100% | 31 | CE | 3 | 50%–60% PPO | 40 | 12 | 2 |
| INT (10) | 60/40 | 59 | 90% | 35 | CE | 3 | 100%–120% PPO × 30 seconds followed by 30 seconds of rest | 40 | 12 | ||
| Freyssin et al | MCT (14) | NR/86 | 55 | 50% | 31 | CE, TM | 5 | HR at VT 1 + gym | 360 min/week | 8 | 2 |
| INT (12) | NR/83 | 54 | 50% | 28 | CE | 5 | 80%–120% PPO × 30 seconds followed by 1 minute of rest × 12 times + gym | 168 min/week | 8 | ||
| Fu et al | MCT (13) | 27/60 | 66 | 62% | 39 | CE | 3 | 60% peak V o 2 | 30 | 12 | 1 |
| INT (14) | 20/67 | 68 | 64% | 38 | CE | 3 | 80% peak V o 2 × 3 minutes followed by 3 minutes at 40% peak V o 2 × 5 | 30 | 12 | ||
| Iellamo et al | MCT (8) | 0/100 | 63 | 100% | 32 | TM | 2–5 | 45%–60% HRR | 30–45 | 12 | 2 |
| INT (8) | 0/100 | 62 | 100% | 34 | TM | 2–5 | 75%–80% HRR × 4 minutes followed by 4 minutes at 45%–50% HRR × 4 | — | 12 | ||
| Nechwatal et al | MCT (18) | 70/30 | 47 | 95% | 27 | CE | 6 | 75% maximal HR (maximal PO 55 W) | 15 | 3 | 2 |
| INT (17) | 70/30 | 45 | 90% | 29 | CE | 6 | 30 seconds at 35%–50% PO from SRT followed by 1 minute recovery (maximal interval and recovery PO 74 and 34 W, respectively) | 15 | 3 | ||
| Smart and Steele | MCT (13) | NR/70 | 63 | 100% | 30 | CE | 3 | 70% peak V o 2 | 30 | 16 | 1 |
| INT (10) | NR/50 | 59 | 80% | 27 | CE | 3 | 70% peak Vo 2 (1 minute exercise and rest) | 60 | 16 | ||
| Wisloff et al | MCT (8) | 0/100 | 74 | 88% | 33 | TM | 3 | 70%–75% peak HR | 47 | 12 | 3 |
| INT (9) | 0/100 | 77 | 78% | 28 | TM | 3 | 90%–95% peak HR × 4 minutes followed by 50%–70% peak HR × 4 | 38 | 12 | ||
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