Effects of strength training on isometric muscle strength and muscle cross-sectional area in adults with a Fontan circulation: a pilot study

Background Adults with complex congenital heart disease, particularly those with a Fontan circulation, often have impaired muscle strength and reduced muscle mass from early age. Despite these concerns, data regarding the effects of strength training in this population is limited. Aim To evaluate the impact of a 10-week strength training intervention on muscle strength and muscle cross-sectional area (CSA) in adults with Fontan circulation, compared to age- and sex matched controls. Methods Nine adults with a Fontan circulation (median age 28.9 [IQR: 23.4-35.0], 4 women) underwent a gym-based strength training program. Isometric muscle strength (elbow flexion, knee extension, grip strength), radial and tibial muscle CSA and density, and habitual physical activity (accelerometer-based and self-reported data) were measured pre- and post-intervention. Within-group changes were analysed using the Wilcoxon signed-rank test; between-group differences were assessed using the Mann Whitney U test. Results Both patients and controls demonstrated improvements in isometric elbow flexion strength (Patients: +6.2% [IQR: 2.8-17.7], p =0.02, r=0.77; Controls: +8.4% [IQR: 2.9-16.0], p =0.012, r=0.84) and tibial cross-sectional area (Patients: +5.0% [IQR: 2.7-11.4], p=0.011, r=0.85; Controls: +4.0% [IQR: 1.4-7.4], p=0.018, r=0.89). No changes were observed in isometric knee extension or grip strength. There were no differences between groups, and no adverse events occurred. Conclusion This pilot study supports that strength training is safe and effective in improving muscle strength and muscle CSA in adults with a Fontan circulation. Despite the small sample size these findings are reassuring. However, confirmation in larger prospective trials is warranted. ClinicalTrials gov, ID: NCT05454254, https://clinicaltrials.gov