High-intensity interval training versus moderate-intensity continuous training on patient quality of life in cardiovascular disease: a systematic review and meta-analysis – Scientific Reports

Search results

Figure 1 displays a flowchart of the literature screening. A total of 5798 articles were retrieved, and after excluding duplicate literature using a literature management software, 3923 articles remained. A total of 659 articles were included in the preliminary screening of their title and abstract. After full-text screening, 633 articles were excluded, leaving 25 remaining. A total of 25 studies were included in this systematic review^{12,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46}, of which 23 were included in the meta-analysis^{12,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,40,41,42,43,45,46}.

Study characteristics

The characteristics of the included studies are summarized in Table 1. The included studies were from 12 different countries, with Canada^25,29,39,47 and Norway^27,38,44,45 dominating the origin of articles. All articles were written in English, except for one published in China that was written in Chinese³⁵. Three studies included were randomized controlled trials^12,26,32. The study participants were predominantly (11/25 studies) patients with coronary heart disease. The remaining studies involved patients with HF^24,26,38,43, tetralogy of Fallot¹², heart transplantation^27,36, coronary artery bypass grafting⁴⁴, atrial fibrillation⁴⁷, myocardial infarction³⁴, stroke³⁷, and hypertension^35,41. Most of the studies reported the registration numbers, while eight did not^{25,26,32,34,42,43,44,46}.

Exercise intervention characteristics

Table 2 shows the characteristics of the HIIT and MICT exercise programs. The narrative summaries of the exercise interventions are as follows: With the exception of 5 studies that did not mention the intervention sites^{12,25,27,35,40}, 3 were conducted at home^31,34,44, 14 at the hospital and rehabilitation center^{24,26,28,29,33,36,37,38,39,42,43,44,46,47}, and the remaining studies were conducted the firm, university, or indoor tennis court^30,32,41. Exercise was conducted under supervision in all studies except two^34,41, and three studies did not report information regarding supervision^12,28,33. Two studies did not report data on adherence to exercise^34,41, while in the remaining studies, exercise adherence ranged 67.1–99.0%^{12,24,25,26,27,28,29,30,31,32,33,35,36,37,38,39,40,42,43,44,45,46}. Adverse events during the exercise interventions were reported in 19 studies^{12,24,27,29,31,32,33,34,36,38,39,40,42,43,44,45,46,47} and of the two reported adverse exercise events^29,31. In all but two studies^26,31, warm-up or relaxation exercises were involved in the exercise program. The frequency of exercise was mainly 2–3 days per week, the exercise duration ranged 20–65 min, and the intervention duration ranged 4–52 weeks.

Methodological quality

The details of the quality assessment are summarized in Fig. 2. In the quality assessment, three differences appeared between researchers regarding two studies^31,33, involving random sequence generation, assignment hiding, and blind setting of outcome evaluators. All of these issues were resolved after discussion among researchers. The consistency among the evaluators was as follows: Kappa value, 0.961; weighted Kappa value, 0.968; and intraclass correlation coefficient, 0.979 (two-way random, absolute agreement). However, there were some methodological flaws among blinded participants and interventionists, and these studies were rated as having a high risk of bias.

GRADE of evidence

According to the Grading of Recommendations and Assessment Development and Evaluation (GRADE) evidence summary, the certainty of QOL, physical component summary (PCS), mental component summary (MCS), and anxiety was moderate, but the certainty of depression was low. Detailed results are shown in Supplement 2.

Outcomes

QOL

QOL was reported in 10 of the 23 included studies^{24,26,28,30,31,33,34,40,43,45}. The effect size synthesis was performed using the standardized mean difference (SMD) in the meta-analysis. There was significant heterogeneity between studies (I² = 79.9%, P < 0.001). The RE analysis showed that the difference in QOL levels between the HIIT and MICT groups was not statistically significant (SMD = 0.21, 95% CI  − 0.18 ~ 0.61, Z = 1.06, P = 0.290), as shown in Fig. 3.

The results of meta-analyses of the effect of quality of life. The results of HIIT and MICT are shown as: mean, standard deviation (sample size).

PCS

PCS levels were reported in 12 of the 23 studies^{12,25,27,29,32,33,36,37,41,42,46,47}. The SMD was used in the meta-analysis for effect size synthesis, and no between-study heterogeneity was detected (I² = 0.00%, P = 0.730). The FE analysis showed that the difference in PCS levels between the HIIT and MICT groups was not statistically significant (SMD = 0.10, 95% CI  − 0.03 ~ 0.23, Z = 1.52, P = 0.128). However, the subgroup analysis showed that, in patients with coronary heart disease, PCS was significantly higher in the HIIT group compared to the MICT group (SMD = 0.23, 95% CI  0.05 ~ 0.41, Z = 2.45, P = 0.014), as shown in Fig. 4.

The results of meta-analyses of the effect of physical component summary. The results of HIIT and MICT are shown as: mean, standard deviation (sample size).

MCS

MCS levels were reported in 12 of the 23 studies^{12,25,27,29,32,33,36,37,41,42,46,47}. The SMD was used in the meta-analysis for effect size synthesis, and low heterogeneity was observed between studies (I² = 18.6%, P = 0.261). The FE analysis showed that the difference in MCS levels between the HIIT and MICT groups was not statistically significant (SMD = 0.07, 95% CI  − 0.05 ~ 0.20, Z = 1.13, P = 0.259), as shown in Fig. 5.

The results of meta-analyses of the effect of mental component summary. The results of HIIT and MICT are shown as: mean, standard deviation (sample size).

Depression

Depression levels were reported in 5 of the 23 studies^{27,29,30,36,38}. The SMD was used in the meta-analysis for effect size synthesis, and significant heterogeneity was detected between the studies (I² = 53.5%, P = 0.072). The FE analysis showed that the difference in depression levels between the HIIT and MICT groups was not statistically significant (SMD = − 0.08, 95% CI  − 0.40 ~ 0.25, Z = − 0.46, P = 0.646), as shown in Fig. 6.

The results of meta-analyses of the effect of depression. The results of HIIT and MICT are shown as: mean, standard deviation (sample size).

Anxiety

Anxiety levels were reported in 4 of the 23 studies^27,30,36,38. The WMD was used in the meta-analysis for effect size synthesis, and no between-study heterogeneity was observed (I² = 0.0%, P = 0.832). The FE analysis showed that the difference in anxiety levels between the HIIT and MICT groups was not statistically significant (WMD = 0.14, 95% CI  − 0.56 ~ 0.84, Z = 0.39, P = 0.694), as shown in Fig. 7.

The results of meta-analyses of the effect of anxiety. The results of HIIT and MICT are shown as: mean, standard deviation (sample size).

Additional analyses

In addition to PCS and MCS, this study conducted additional analyses of sub-indicators for eight dimensions of quality of life: physical functioning (PF), role-physical (RP), bodily pain (BP), general health (GH), vitality (VT), social functioning (SF), role-emotional (RE), MH, and reported health transition (HT). Ten of the 23 studies reported, in detail, on the eight sub-dimensions of SF-36 and SF-12^{25,28,29,32,33,35,36,41,47}. Therefore, additional analyses were performed on these dimensions. Surprisingly, the HIIT group was superior to the MICT group for three dimensions, namely RP, VT, and SF, and the differences were statistically significant. The results of the meta-analysis for RP (SMD = 0.23, 95% CI  0.04 ~ 0.41, Z = 2.36, P = 0.018) and the FE analysis of VT (SMD = 0.22, 95% CI  0.04 ~ 0.39, Z = 2.46, P = 0.014), and SF (SMD = 0.17, 95% CI  0.00 ~ 0.35, Z = 1.98, P = 0.048) are shown in Table 3 and Fig. 8, and further details are displayed in Supplement 3.

The results of meta-analyses of the effect of eight sub-dimensions in QOL. The results of HIIT and MICT are shown as: mean, standard deviation (sample size).

Sensitivity analyses

In the sensitivity analyses for QOL, PCS, MCS, depression, and anxiety, after each of the included studies were excluded one-by-one, the overall effect values of the remaining studies fell within the 95% CI range of the original overall effect value, indicating that the meta-analysis results for QOL, PCS, MCS, depression, and anxiety were highly stable and contained no influential studies, as shown in Fig. 9.

The results of sensitivity analyses.

Publication bias

Publication bias was assessed regarding QOL, PCS, and MCS. In the funnel plot of QOL, results were distributed on both sides of the symmetry axis. The funnel plots appeared to be asymmetric, suggesting that publication bias may exist in the data regarding QOL; however, the results of the egger test showed no publication bias (t = 1.21, P = 0.260). In the results both of PCS and MCS, the funnel plots were symmetric, suggesting that the data for PCS and MCS were not influenced by publication bias, as supported by the results of the egger test (t = − 1.89, P = 0.087 and t = 0.76, P = 0.466, respectively). According to the principle of inclusion and testing of publication bias, the analysis did not include depression and anxiety due to the limited availability of literature, with less than 10 studies available^48,49, as shown in Fig. 10.

The results of publication bias.