Although current clinical guidelines stipulate that patients with hypertrophic cardiomyopathy should not partake in high intensity exercise (HIE) or competitive sport due to safety concerns, there is no clear evidence to support this notion. In fact, two exercise training interventions in this population indicates that regular moderate to vigorous intensity exercise is efficacious for improving exercise capacity and cardiorespiratory fitness, and does not increase arrhythmia burden or adverse events. Moreover, moderate intensity exercise and HIE training significantly increases cardiorespiratory fitness in patients with cardiac disease. Such improvements are associated with substantial reductions in cardiovascular mortality and might outweigh the risk of adverse events in patients with hypertrophic cardiomyopathy (HCM). Having a genetic cardiomyopathy does not grant immunity against lifestyle related cardiometabolic diseases and inactivity is rife in HCM patients likely due to misinformation/education. It is therefore paramount to further explore the benefits of regular moderate intensity exercise and HIE in patients with HCM for proper therapeutic management of the condition.

Regular exercise reduces the risk of all-cause and cardiovascular mortality in the general population. Specifically, higher cardiorespiratory fitness is associated with a 10 - 20 % reduction in mortality risk for every 1 MET (metabolic equivalent tasks) improvement in fitness. A high degree of fitness is also protective against the development of heart failure and exercise training has become the standard of care for most patients with cardiovascular disease to improve functional capacity, and reduce morbidity and mortality. However, hypertrophic cardiomyopathy, the most common inherited cardiovascular disease, may be an exception. For more than 30 years, hypertrophic cardiomyopathy (HCM) has been identified as the most common cause of death in young athletes, and patients with HCM are excluded from participation in competitive sports. The fear of provocation of sudden cardiac death has often been extended to non-competitive athletic activities in such patients, though there is a distinct lack of evidence about the safety of exercise in this population. A recent multicenter clinical trial provided evidence that moderate intensity exercise (MIE) may be safe in this population, though the increase in fitness with this training paradigm was modest. Alternatively, an extensive series of reviews published over the last five years advocate for high intensity interval training (HIIT) as an efficacious stimulus for increasing cardiorespiratory fitness in clinical adult populations, including those with heart failure. While a pilot investigation and preliminary findings suggest that moderate to vigorous intensity exercise may be safe and efficacious in patients with HCM, and even protective in animal models, there is no Level A or B evidence comparing the efficacy or safety of MIE and high intensity exercise (HIE) training in this patient population to guide exercise prescription. Therefore, the primary purpose of this exercise trial is to compare the efficacy and safety of supervised MIE and HIE training in adults with HCM. Specific aims and hypotheses of the project are as follows:

Aim 1: Compare the efficacy of a high intensity and moderate intensity exercise intervention to improve cardiorespiratory fitness and functional diastolic reserve in patients with HCM.

• Primary hypothesis: HIE will result in greater increases in maximal oxygen uptake (V̇O2max) than MIE in patients with HCM.
• Secondary hypothesis: HIE will improve stroke volume reserve to a greater degree than MIE in patients with HCM.

Aim 2: To evaluate the safety of HIE training in patients with HCM.

• Hypothesis: Regular exercise training of a high or moderate intensity will be safe (no serious adverse events) in this patient population. Specifically, it is hypothesised that HIE will not increase arrhythmia burden in patients with HCM.

Inclusion Criteria:

• Male and female patients aged 18 - 80 years old
• Diagnosed HCM defined by the presence of unexplained left-ventricular hypertrophy with end-diastolic wall thickness ≥ 15 mm on 2D echocardiography or wall thickness between 13 and 15 mm along with at least one other piece of evidence of hypertrophic cardiomyopathy, such as systolic anterior motion of the mitral valve leaflets, family history of hypertrophic cardiomyopathy, or positive genetic test result.

Exclusion Criteria:

• A history of exercise-induced syncope or arrhythmias (ventricular tachycardia; sustained or non-sustained)
• Left ventricular outflow obstruction (≥ 50 mm Hg at rest)
• Less than 3 months post septal reduction therapy (surgery or catheter based intervention)
• Pregnancy
• Worsening clinical status or advanced heart failure (New York Heart Association class IV symptoms)
• A hypotensive responsive to exercise (an increase in exercise systolic BP throughout the exercise test of < 20mmHg compared with resting values, or an initial increase in systolic BP > 20mmHg with a subsequent fall by peak exercise of > 20mmHg, or a continuous decrease in systolic BP throughout the test of > 20mmHg, compared with baseline BP)
• Left ventricular systolic dysfunction (left ventricular ejection fraction < 55 % by echocardiography)
• Coronary artery disease as evidenced by prior myocardial infarction or angina
• Cerebrovascular disease as evidenced by prior transient ischemic attack or stroke
• A chronic orthopaedic injury which limits the ability to exercise
• Subjects unable to speak English will not be recruited because of the complex experimental studies and the need for precise communication between the volunteers and the research staff to ensure safety.