OBJECTIVE: To explore the effect sizes of different high-intensity interval training (HIIT) protocols on cardiorespiratory parameters when compared with moderate-intensity continuous training (MICT) in different heart failure (HF) subtypes. DATA SOURCES: Electronic databases were searched from their inception date until January 23, 2023. STUDY SELECTION: Randomized controlled trials (RCTs) were included if they compared HIIT with MICT in patients with HF. The primary outcome was peak oxygen consumption (Vo2peak). Two reviewers independently evaluated 99 initially identified studies, resulting in the selection of 15 RCTs that met the eligibility criteria. DATA EXTRACTION: Data were extracted independently by 2 observers using a data extraction form drafted based on the CONSORT statement and the Template for Intervention Description and Replication; the methodological quality of the studies was analyzed individually based on the Tool for the Assessment of Study Quality in Exercise scale. DATA SYNTHESIS: Fifteen RCTs with 553 patients with HF were included in the systematic review. The included studies had moderate to good overall methodological quality. The results showed that HIIT was generally more effective than MICT at improving Vo2peak in patients with HF (n = 541, 15 RCTs; MD 1.49 mL/kg/min; I2 66%; p < 0.001). However, the effect size varied depending on the HF subtype and HIIT protocol used. For patients with HF with reduced ejection fraction (HFrEF), the long-interval (high-intensity interval lasting >= 4 min) and high-volume HIIT (high-intensity efforts in total >= 15 min) showed the largest benefits over the MICT (n = 261, 6 RCTs; MD 2.11 mL/kg/min; p < 0.001); followed by the short-interval (<= 1 min) and high-volume HIIT (>= 15 min; n = 71, 3 RCTs; MD 0.91 mL/kg/min; p = 0.12), and the short-interval and low-volume HIIT showed the least superiority over MICT (n = 68, 3 RCTs; MD 0.54 mL/kg/min; p = 0.05). For patients with HF with perceived ejection fraction, there was a modest beneficial effect from HIIT over MICT (n = 141, 3 RCTs; MD 0.55 mL/kg/min; p = 0.32). CONCLUSIONS: The long-interval and high-volume HIIT protocol may produce greater benefits than MICT for improving cardiopulmonary fitness in patients with HFrEF. Further research is needed to determine the optimal HIIT protocol for different HF subtypes and to provide definitive recommendations for clinical practice.

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