10 adults with Fontan circulation will be recruited from the clinic specialised in adults with congenital heart disease at Norrlands Universitetssjukhus. In addition, 10 age- and sex matched controls will be recruited. The sample size is estimated according to a previous study with the same primary outcome. We estimate that 7 patients and 7 controls are needed in the study and plan to enrol 10 patients and 10 controls in case of any drop outs.~Muscle tests will be performed at baseline. Based on the results from the muscle tests, an individualised muscle training exercise protocol will be designed and the participants will be working out at a gym during 10 weeks. After 10 weeks the same tests will be performed to evaluate the effect of the muscle training exercise.~In addition to the muscle tests, muscle mass and aerobic exercise capacity will be evaluated with peripheral quantitative computed tomography and cardiopulmonary exercise test respectively. Physical activity will be mapped with a validated questionnaire (IPAQ) and an accelerometer attached to the participants thigh. Any impact on fatigue will be evaluated with a validated questionnaire (MFI-20). All tests and questionnaires will be performed at baseline and at follow-up.
Aim: to evaluate the effect of muscle strengthening exercise training in adults with Fontan circulation compared to healthy controls.~Hypothesis: adults with Fontan circulation have a relatively lower effect of muscle strengthening exercise training compared to healthy controls.