Heart failure (HF) affects more than 60 million people worldwide and remains a leading cause of hospitalization, disability, and death despite advances in pharmacological and device-based therapy.^1,2 Beyond impaired cardiac function, chronic HF is characterized by a progressive decline in exercise tolerance, skeletal-muscle deconditioning, and reduced health-related quality of life, all of which contribute to the symptom burden patients experience. Exercise-based cardiac rehabilitation has therefore become a cornerstone of contemporary HF management. Landmark trials and meta-analyses — including the HF-ACTION study and the ExTraMATCH collaboration — have shown that structured exercise training improves functional capacity, reduces hospitalization, and is safe in clinically stable patients.^3,4 Accordingly, current European and American guidelines assign exercise training a class I recommendation in chronic HF.^1,2

Peak oxygen uptake (peak VO₂) measured during cardiopulmonary exercise testing is among the most powerful prognostic markers in HF and a principal target of aerobic conditioning.⁵ Historically, continuous and interval aerobic training has dominated rehabilitation protocols because of its well-established effects on central haemodynamics, peripheral oxygen extraction, and endothelial function.⁶ However, the skeletal-muscle myopathy of HF — marked by fibre-type shifts, reduced oxidative capacity, and loss of muscle mass — also drives fatigue, weakness, and exercise intolerance, and is not fully addressed by aerobic training alone.⁷ This recognition has stimulated interest in resistance (strength) training as a complementary or alternative modality.

Resistance training directly targets neuromuscular adaptation, increasing muscle strength, mass, and functional independence, and is now endorsed within cardiac rehabilitation when applied with appropriate supervision.⁸ Yet concerns about haemodynamic loading historically limited its use in HF, and the comparative efficacy of aerobic versus resistance training across the full spectrum of clinically relevant outcomes — functional capacity, cardiopulmonary fitness, muscle strength, and quality of life — remains poorly defined.⁹ Most prior studies have examined a single domain or used combined-training designs, leaving clinicians without clear head-to-head evidence to guide modality selection for individual patients.

We hypothesized that aerobic and resistance training would each produce domain-specific benefits consistent with the principle of training specificity: aerobic training yielding superior improvements in walking distance and peak VO₂, and resistance training yielding superior gains in muscle strength and, potentially, quality of life. To test this hypothesis, we conducted a 12-week, parallel-group randomized controlled trial directly comparing supervised aerobic with supervised resistance training in patients with chronic stable HF (NYHA II–III) on optimized medical therapy. The primary outcome was change in 6-minute walk test distance, with peak VO₂, muscle strength, KCCQ-assessed quality of life, and safety as secondary outcomes. By evaluating several domains within a single trial, we aimed to provide a clinically actionable evidence base for individualized exercise prescription in HF.

Study design and setting. This was a single-centre, prospective, parallel-group, two-arm randomized controlled trial conducted at a tertiary cardiac rehabilitation unit over a 12-week intervention period. The study was performed in accordance with the Declaration of Helsinki and approved by the institutional ethics committee; all participants provided written informed consent before enrolment. Participants. Adults with chronic stable HF of NYHA functional class II–III, on guideline-directed medical therapy stable for at least four weeks, were eligible. Both HF with reduced ejection fraction (HFrEF, LVEF ≤40%) and HF with preserved ejection fraction (HFpEF) were included. Key exclusion criteria were decompensated HF, recent (<3 months) acute coronary syndrome or revascularization, severe or uncorrected valvular/congenital disease, uncontrolled arrhythmia, and any orthopaedic or neurological condition precluding safe exercise. Of 168 patients screened, 140 met the eligibility criteria and were enrolled. Randomization and blinding. Participants were allocated 1:1 to aerobic training (Group A, n=70) or resistance training (Group B, n=70) using a computer-generated random sequence with concealed allocation. Outcome assessors and the data analyst were blinded to group assignment; supervising exercise physiologists could not be blinded. Interventions. Both programmes comprised three supervised sessions per week for 12 weeks, each with a 5–10-minute warm-up and cool-down. The aerobic group performed continuous and interval treadmill or cycle-ergometer exercise at 60–70% of heart-rate reserve, progressing in duration from 20 to 40 minutes as tolerated, with intensity guided by the Borg scale and telemetry. The resistance group performed progressive whole-body resistance exercise targeting major upper- and lower-limb muscle groups (8–10 exercises, 2–3 sets of 10–15 repetitions) at 50–70% of one-repetition maximum (1-RM), with loads advanced as strength improved. All sessions were supervised with cardiac monitoring and resuscitation facilities available. Outcomes and measurements. The primary outcome was change in 6-minute walk test (6MWT) distance from baseline to 12 weeks, performed per American Thoracic Society guidelines.10 Secondary outcomes were peak VO₂ on symptom-limited cardiopulmonary exercise testing; muscle strength by handgrip dynamometry and upper- and lower-limb 1-RM; health-related quality of life by the Kansas City Cardiomyopathy Questionnaire (KCCQ) overall summary score;11 and safety (adverse events and HF-related hospitalizations). Assessments were performed at baseline, 6 weeks, and 12 weeks. Sample size and statistics. The sample size was calculated to detect a clinically important between-group difference of approximately 30 m in 6MWT distance, incorporating 10% anticipated attrition. Continuous variables are presented as mean ± SD or median (IQR) and categorical variables as n (%). Between-group comparisons used independent t-tests, chi-square or Fisher's exact tests, and Mann–Whitney U tests as appropriate; within-group changes used paired t-tests. Multivariable linear regression adjusted for age, sex, and baseline LVEF. A two-sided p<0.05 was considered significant.

Participant flow and baseline characteristics

A total of 168 patients with chronic stable heart failure (NYHA class II–III) were screened, of whom 140 met the eligibility criteria and were randomized 1:1 to aerobic training (Group A, n=70) or resistance training (Group B, n=70). Seven patients in each group were lost to follow-up or discontinued the intervention, leaving 63 patients per group (n=126) for the final 12-week analysis, a retention rate of 90% consistent with the 10% attrition anticipated in the sample-size calculation (Figure 1).

Figure 1. CONSORT flow diagram showing screening, randomization, allocation, and follow-up of study participants.

Baseline demographic and clinical characteristics were well balanced between the two groups, confirming successful randomization (Table 1). Mean age, sex distribution, NYHA class, ejection-fraction phenotype, aetiology, and NT-proBNP did not differ significantly between groups (all p>0.05), indicating that any 12-week between-group differences are unlikely to reflect baseline imbalance.

Table 1. Baseline demographic and clinical characteristics.

Values are mean ± SD, n (%), or median (IQR). p-values from independent t-test, chi-square test, or Mann–Whitney U test. BMI = body mass index; LVEF = left ventricular ejection fraction; HFrEF = HF with reduced ejection fraction; HFpEF = HF with preserved ejection fraction; NYHA = New York Heart Association.

Baseline functional capacity (6-minute walk test [6MWT] distance, peak VO₂), muscle strength, and Kansas City Cardiomyopathy Questionnaire (KCCQ) scores were likewise comparable, with no significant between-group differences for any parameter (Table 2).

Table 2. Baseline functional capacity, muscle strength, and quality-of-life parameters.

Values are mean ± SD. P-values from independent t-test. 6MWT = 6-minute walk test; 1-RM = one-repetition maximum; KCCQ = Kansas City Cardiomyopathy Questionnaire; SBP = systolic blood pressure.

Primary outcome: 6-minute walk test distance

Both groups achieved highly significant within-group improvements in 6MWT distance from baseline to 12 weeks (paired p<0.001 for both). The mean gain was greater after aerobic training (+60 m) than after resistance training (+40 m), and this between-group difference was statistically significant at both 6 weeks (p=0.04) and 12 weeks (p=0.01), exceeding the pre-specified clinically important difference of approximately 30 m (Table 3, Figure 2).

Table 3. Change in 6-minute walk test distance (primary outcome).

Between-group comparison by independent t-test; within-group comparison by paired t-test. SD = standard deviation.

Figure 2. Trend in 6-minute walk test distance from baseline to 12 weeks in both groups (mean ± SD).

Cardiopulmonary fitness: peak VO₂

Peak VO₂ increased significantly in both groups (within-group p<0.001). The improvement was substantially larger after aerobic training (+3.6 mL/kg/min, +24.3%) than after resistance training (+1.7 mL/kg/min, +11.6%), with the between-group difference significant at 6 weeks (p=0.002) and 12 weeks (p<0.001) (Table 4, Figure 3). This pattern is consistent with the physiological specificity of aerobic conditioning for central and peripheral oxygen utilization.

Table 4. Change in peak VO₂ on cardiopulmonary exercise testing.

Values in mL/kg/min. SD = standard deviation; CPET = cardiopulmonary exercise testing.

Figure 3. Trend in peak VO₂ from baseline to 12 weeks in both groups (mean ± SD).

Muscle strength

Muscle strength, assessed by handgrip dynamometry and limb 1-RM testing, improved significantly in both groups, but the gains were considerably larger after resistance training. Handgrip strength rose by 34.4% in Group B versus 11.3% in Group A (between-group p<0.001), with a parallel pattern for upper- and lower-limb 1-RM (Table 5, Figure 4). These results reflect the neuromuscular specificity of progressive resistance loading.

Table 5. Change in muscle strength parameters.

Percentages denote relative change from baseline to 12 weeks within each group. 1-RM = one-repetition maximum.

Figure 4. Trend in handgrip strength from baseline to 12 weeks in both groups (mean ± SD).

Health-related quality of life

Both groups improved significantly in KCCQ overall summary score, each exceeding the established 5-point minimal clinically important difference. The resistance group showed a larger improvement (+22.1 points, +41.1%) than the aerobic group (+17.3 points, +31.9%); the between-group difference was significant at 12 weeks (p=0.03) (Table 6, Figure 5). This suggests an additional quality-of-life benefit from resistance-based training, plausibly mediated by improved functional independence and reduced symptom burden related to muscle weakness.

Table 6. Change in quality of life (KCCQ overall summary score).

KCCQ range 0–100; higher = better. SD = standard deviation.

Figure 5. Trend in KCCQ overall summary score from baseline to 12 weeks in both groups (mean ± SD).

Relative improvement across outcome domains

Table 7 and Figure 6 summarize the relative (percentage) improvement across all major domains, revealing a consistent, modality-specific pattern: aerobic training produced greater relative gains in cardiopulmonary measures (6MWT distance, peak VO₂), whereas resistance training produced greater relative gains in musculoskeletal and quality-of-life measures (handgrip strength, KCCQ).

Table 7. Summary of percentage improvement across key outcomes at 12 weeks.

Percentage change = (12-week value − baseline value) / baseline value × 100.

Figure 6. Percentage improvement in key outcome measures at 12 weeks, by training modality.

Safety

Both modalities were well tolerated. Mild musculoskeletal discomfort was the most common adverse event and occurred more frequently with resistance training (11.1% vs 6.3%), though not significantly (p=0.34); exercise-induced hypotension was more common with aerobic training. No deaths occurred, and HF-related hospitalization was low and similar between groups (Table 8, Figure 7), supporting the safety of both supervised modalities in clinically stable patients on optimized therapy.

Table 8. Adverse events and hospitalizations during the intervention period.

Values are n (%). p-values from chi-square or Fisher's exact test. HF = heart failure.

Figure 7. Number of adverse events and hospitalizations by category and training group during the 12-week intervention period.

Multivariable analysis

On multivariable linear regression adjusting for age, sex, and baseline LVEF, training modality (resistance vs aerobic) remained an independent predictor of change in handgrip strength (β=5.8, 95% CI 3.9–7.7; p<0.001) and change in KCCQ score (β=4.6, 95% CI 1.2–8.0; p=0.008), while aerobic training remained an independent predictor of change in peak VO₂ (β=1.9, 95% CI 1.1–2.7; p<0.001) and change in 6MWT distance (β=18.4, 95% CI 6.2–30.6; p<0.001). The modality-specific effects therefore persisted after adjustment for these baseline confounders.

In this randomized comparison of aerobic versus resistance training in chronic stable HF, both modalities produced significant 12-week improvements across functional, cardiopulmonary, neuromuscular, and quality-of-life domains, but with a clear and physiologically coherent pattern of modality specificity. Aerobic training produced greater gains in 6MWT distance and peak VO₂, whereas resistance training produced greater gains in muscle strength and quality of life. These findings extend prior work by demonstrating, within a single head-to-head trial, that the choice of exercise modality systematically shapes which clinical benefits predominate. The superior aerobic effect on peak VO₂ (+3.6 vs +1.7 mL/kg/min) is consistent with the established physiology of endurance conditioning, which enhances cardiac output, mitochondrial density, and peripheral oxygen extraction.6 Because peak VO₂ is a robust prognostic marker in HF,5 this magnitude of improvement is clinically meaningful and aligns with the functional-capacity benefits reported in HF-ACTION and ExTraMATCH.3,4 The parallel 6MWT advantage reinforces aerobic training's role where the therapeutic priority is exercise tolerance and walking capacity. Conversely, resistance training produced markedly greater strength gains (handgrip +34.4% vs +11.3%), reflecting the neuromuscular specificity of progressive loading and directly countering the skeletal-muscle myopathy that characterizes HF.7 Importantly, resistance training also yielded a larger KCCQ improvement (+22.1 vs +17.3 points), with both groups exceeding the 5-point minimal clinically important difference.12 This quality-of-life advantage may be mediated by improved functional independence and reduced symptom burden associated with greater muscle strength, and accords with meta-analytic evidence that resistance training improves strength and quality of life without compromising aerobic capacity in HF.13 Persistence of modality effects after adjustment for age, sex, and baseline LVEF supports their independence from baseline confounders. Both interventions were safe: there were no deaths, hospitalization rates were low and similar, and adverse events — predominantly mild musculoskeletal discomfort (slightly more frequent with resistance training) and exercise-induced hypotension (more frequent with aerobic training) — were well tolerated. These data are reassuring and consistent with contemporary recommendations endorsing supervised resistance exercise in appropriately selected cardiac patients.8 Taken together, the results argue against a one-size-fits-all approach: patients whose principal limitation is breathlessness and low exercise capacity may be prioritized for aerobic training, whereas those with prominent weakness, frailty, or impaired quality of life may derive greater benefit from resistance training. The complementary nature of these effects provides a strong rationale for combined aerobic-plus-resistance programmes. This study has limitations. It was single-centre with a 12-week horizon, limiting inference about long-term outcomes, hospitalization, and mortality; the exercise physiologists could not be blinded; and combined-training and usual-care arms were not included. Larger multicentre trials with longer follow-up and hard clinical endpoints are needed to confirm whether modality-specific functional gains translate into durable prognostic benefit.

Among patients with chronic stable HF on optimized therapy, 12 weeks of supervised aerobic and resistance training were both safe and effective but conferred distinct, modality-specific benefits: aerobic training maximized cardiopulmonary fitness and walking capacity, whereas resistance training maximized muscle strength and quality of life. These findings support individualized exercise prescription tailored to each patient's dominant limitation and provide a rationale for combined training to address the full spectrum of impairment in HF.

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