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Background: Impaired muscle function, aerobic capacity, and fatigue are common in individuals with Fontan circulation. Knowledge regarding the effects of strength training in this population is limited. Therefore, the study aimed to investigate the effects of strength training on dynamic muscle function, aerobic capacity, and fatigue in adults with Fontan circulation compared to matched controls.

Methods: In this pilot non-randomised controlled trial, nine patients with Fontan circulation (median age 28.9 years [IQR: 23.4-35.0], 44.4% women) and nine age- and sex-matched controls completed a 10-week strength training intervention. Dynamic muscle function was assessed through shoulder flexion, heel rise, elbow flexion, and knee extension tests. Aerobic capacity was evaluated using cardiopulmonary exercise testing, and fatigue using the questionnaire Multidimensional Fatigue Inventory. All assessments were conducted pre- and post-intervention. Within-group changes were analysed using the Wilcoxon signed rank test and between-group differences using the Mann-Whitney U test.

Results: Patients showed improvements in all muscle function tests post-intervention (shoulder flexions 39.3% [IQR: 18.9-69.7], p = 0.008; heel rise 26.7% [IQR:17.5-58.1], p = 0.008; elbow flexions 57.1% [IQR: 50.0-173.8], p = 0.007; knee extensions 66.7% [24.3-92.9], p = 0.008). The improvements were at comparable levels to controls. Only controls reported reduced fatigue (-19.4% [IQR: -28.7, -10.5], p = 0.01), while patients showed no change (-5.9% [IQR: -25.5, 3.2], p = 0.1). Aerobic capacity remained unchanged. No severe adverse events occurred.

Conclusion: Strength training is safe and improves dynamic muscle function in patients with Fontan circulation, with changes comparable to those of healthy controls. However, the effect of strength training on fatigue and aerobic capacity requires further investigation. ClinicalTrials.gov, ID: NCT05454254, https://clinicaltrials.gov.