Inspiratory muscle training as an adjunct to standard cardiac rehabilitation in patients with LVEF < 50%: a randomized controlled trial

Impaired inspiratory muscle strength is prevalent in heart failure (HF). Despite standard aerobic and resistance training, patients often experience residual exercise intolerance. Adding inspiratory muscle training (IMT) appears promising, but its aprecise additive value remains unclear, particularly in contemporary cohorts with LVEF < 50%. We randomized 65 HF patients (LVEF < 50%) to standard aerobic and resistance training (AR group, n = 32; 60 min/session) or AR plus IMT (ARIS strategy, n = 33; 90 min/session). Both protocols prescribed 36 sessions (3 sessions/week for 12 weeks). The primary outcome was the change in the Kansas City Cardiomyopathy Questionnaire (KCCQ) Overall Summary Score. Data were analyzed according to the intention-to-treat (ITT) principle. Full completion of all 36 prescribed sessions was achieved by 53.1% (AR) and 57.6% (ARIS) of patients, yielding an actual time-adjusted training density of 2.38 and 2.53 sessions/week, respectively. In the primary outcome analysis, the ARIS strategy demonstrated greater KCCQ Overall Summary Score improvement (between-group difference: +6.3 points; P = 0.006), exceeding the minimal clinically important difference (MCID) of 5 points. The ARIS strategy also yielded significantly greater increases in 6-minute walk distance (+ 33.9 m; P = 0.016) and maximal inspiratory pressure (+ 2.0 kPa; P < 0.001). Regarding cardiac structure, no significant between-group differences were observed for changes in LVEF (P = 0.818) or left ventricular end-diastolic volume (LVEDV) (P = 0.990). In HF patients (LVEF < 50%), the extended multimodality ARIS strategy provides clinically significant improvements in quality of life and functional capacity compared to standard training. These incremental benefits likely stem from the combined addition of IMT and higher exercise volume, occurring without significant between-group differences in macro-structural cardiac remodeling. Adequately powered studies are needed to confirm efficacy in the HFmrEF subgroup. Chinese Clinical Trial Registry ChiCTR2500108124. Retrospectively registered on 25 August 2025.