The road to strength: functional progress after rehabilitation

Abstract Introduction Increasing evidence supports that greater muscle strength is associated with reduced cardiovascular mortality and morbidity. However, the relationship between muscle strength, physical activity, and cardiopulmonary performance during cardiac rehabilitation has not been fully clarified. Objective To analyze the evolution of muscle strength in patients undergoing a phase II cardiac rehabilitation program and investigate the correlation between muscle strength, functional capacity assessed by cardiopulmonary exercise testing (CPET), and other functional measures. Methods Prospective, single-center observational study including patients enrolled in a phase II cardiac rehabilitation program from 2016 to 2024. The evaluation involved standardized assessments: 6-Minute Walk Test (6MWT), International Physical Activity Questionnaire (IPAQ), Timed Up and Go (TUG), and FICSIT Balance Test, along with clinical and CPET data. Muscle strength was assessed through upper and lower limb testing, including bilateral grip strength. Statistical analyses included Pearson correlation and pre- and post-program comparisons. Results 446 patients were included (80% men, mean age 61.1 ± 11.4 years), with multiple cardiovascular risk factors: hypertension (66.8%), diabetes (28.2%), dyslipidemia (70.4%), and history of smoking (61.1%). The most prevalent etiology was ischemic cardiomyopathy (85.2%), with 43.1% presenting single-vessel coronary disease. Post-rehabilitation, significant improvements were observed in multiple endpoints: Functional capacity by 6MWT (444.6 ± 95.8 m to 541.8 ± 102.9 m; p0.001); Physical activity by IPAQ (median 231 to 1406; p0.001); TUG (from 9.3 8.2-10.8 to 7.9 6.9-9.0 seconds; p0.001); FICSIT (from 18.1 ± 6.0 to 23.5 ± 6.4; p0.001); Muscle strength of upper and lower limbs (p0.001 for both); Bilateral grip strength (left: 31.4 ± 9.3 to 34.2 ± 10.3, p0.001; right: 32.8 ± 9.6 to 35.5 ± 10.6, p0.001). Moderate, statistically significant correlations were found between upper and lower limb muscle strength and exercise duration during CPET (r=0.4–0.5, p0.001), and with peak oxygen uptake (VO2 peak) (r=0.4, p0.001). Patients with poor functional capacity post-rehabilitation (VO2 18 mL/kg/min) exhibited significantly lower values across all assessed measures compared to those who achieved ≥18 mL/kg/min, emphasizing the role of VO2 peak as a key discriminator of overall functional status. Conclusion Cardiac rehabilitation was associated with significant increases in muscle strength and improvements in functional and exercise performance. The moderate correlations between muscle strength and CPET parameters, especially VO2 peak, suggest that greater strength contributes to better cardiorespiratory performance. Routine assessment of muscle strength may enhance individualized interventions and help identify patients at higher functional risk