Introduction: The Fontan operation is the surgical treatment in most patients with either anatomic or functional single ventricles. In this operation, the subpulmonary ventricle is bypassed, connecting the systemic veins directly to the pulmonary arteries. The lack of a subpulmonary ventricle is associated with a nonpulsatile pulmonary flow and triggers a sequence of adaptive mechanisms along the life of these patients. The most frequent consequence of these adaptative mechanisms is the reduction in functional capacity, objectively measured by the decrease in peak oxygen consumption (VO2). So, cardiovascular and pulmonary functioning and skeletal muscle alterations can explain exercise intolerance in these patients.

Objectives: 1. To compare the cardiovascular, pulmonary, and musculoskeletal system variables in clinically stable Fontan patients with Healthy subjects; 2. To correlate the variables of the cardiovascular, pulmonary, and skeletal muscle with the functional capacity in Fontan patients; 3. To identify predictors of low functional capacity in this population; 4. To evaluate four-month aerobic exercise and inspiratory muscle training on functional capacity, pulmonary function, and autonomic control in patients after Fontan operation and compare to the group with no exercise training.

Methods: All subjects were submitted to cardiovascular, pulmonary, and skeletal muscle evaluation at baseline to perform a cross-sectional study comparing Fontan Patients (FP) with Healthy Controls (HC). In addition, the FP accepted to participate in the longitudinal clinical trial to evaluate exercise programs were randomized into three groups: Aerobic Exercise Training (AET), Inspiratory Muscle Training (IMT), and Non-exercise Training Group (NET, a control group). All patient groups (AET, IMT, NET) were reassessed after four months of training or under usual care.

Expected Outcomes: This study expects to demonstrate that impaired pulmonary function, altered neurovascular control, and reduced skeletal muscle could be an additional potential mechanism for reducing functional capacity in clinically stable Fontan patients. And this impairment could be diminished by exercise training, enhancing physical capacity, and exercise tolerance.

All subjects were submitted to cardiovascular magnetic resonance, echocardiography, cardiopulmonary exercise test, complete lung function, catecholamine and B-type natriuretic peptide (BNP) plasmatic levels, microneurography, venous occlusion plethysmography, six-minute walk test, phosphorus magnetic resonance spectroscopy (31P MRS) and magnetic resonance imaging (MRI) of skeletal muscle and quality of life (QoL) using the Short Form Health Survey (SF36) in the baseline. Comparative analyzes of the different systems of the two groups were done as well as tests to identify the predictors of low functional capacity in Fontan groups (FG).

The evaluation was done at baseline in healthy subjects. And in the Fontan group at baseline and after four months of exercise training or usual care.

AET Protocol: Four-month supervised exercise training was performed in the hospital three times a week, 60-min exercise sessions (48 sessions in total). Each session consisted of 40min on a treadmill, 15 min of personal light resistance training (including chest press, squat, pull down, leg extension, shoulder press, calf raises, leg curl, and sit-ups), and 5min of cool down and stretching. The AET was individually prescribed according to their heart rate (HR) from maximal cardiopulmonary exercise testing (CPT), and patients exercised between the ventilatory threshold (VT) and respiratory compensation point (RCP). HR, systolic blood pressure, oxygen saturation, and exhaustion (i.e., Borg scale from 7 to 20) were monitored during the sessions. An exercise physiologist supervised all sessions. In the first 12 weeks, HR was maintained at T frequency. Between the 12th to 24thweek, there was a progressive increase in the effort, and HR was supported between AT and RCP. In the last 12 sessions of the program, HR was maintained close to RCP frequency.

IMT Protocol: Four months of exercise training were carried out daily, three sets of 30 repetitions using the POWERbreathe® device (POWERbreathe International Limited, Southam, UK), three sets of 30 repetitions. Maximal inspiratory pressure (MIP) measures were performed in all patients before the intervention, and patients exercised at 60% of individual MIP. Patients were instructed to inhale using diaphragm musculature, trying to expand the rib cage to avoid the use of accessory muscles, and breathing at a rate of 12 to 16 breaths/min. A nose clip was worn to ensure patients breathed exclusively through the training device. All patients had a supervised session of IMT with a physiotherapist once a week for the first two months and once every two weeks for the last two months. The load was adjusted during the supervised sessions. Patients were encouraged to maintain their habitual activities during the protocol.

Inclusion Criteria:

• Both gender, aged between 12 and 30 years
• Patients undergoing the Fontan operation with time postoperatively ≥5 years
• Clinically stable patients, no arrhythmia in the last electrocardiogram or clinical assessment
• Consent by the cardiologist
• Patients who voluntarily signed the consent form.

Exclusion Criteria:

• Patients with hypoplastic left heart syndrome
• Changes that reduce musculoskeletal walking skills
• Neurological sequelae, patients with associated genetic syndrome, disturbance cognitive or psychiatric
• Patients with a history of ventricular arrhythmias, cardio respiratory arrest, users of anti-arrhythmic drugs and / or underwent implantation of pacemaker
• Atrial arrhythmia requiring treatment in the last 6 months
• Patients with heart failure not controlled by medications and lung hypertension
• Patients with protein-losing enteropathy
• Severe hypoxemia (oxygen saturation <80% at rest)
• Symptomatic patients with a diagnosis of diaphragmatic paresis or paralysis postoperative patients, with or without plication
• Patients with moderate to severe asthma
• Patients who live outside the area of Sao Paulo