Hospital discharge > 60 days unless readmitted to hospital in first 30 days, then 60 day window restarts and new exclusion is last hospital discharge > 60 days

Not ambulating independently prior to COVID-19 illness (use of a gait aid permitted)

Functional impairment resulting in inability to exercise at baseline

Inability or unwillingness to comply with the study requirements or unable or unwilling to follow coaching via mobile-health iPhone interaction

Any absolute contraindications to exercise, including but not limited to:

• Recent (< 5 days) acute primary cardiac event
• Unstable Angina
• Uncontrolled dysrhythmias causing symptoms or hemodynamic compromise
• Uncontrolled hypertension over 255 mmHg Systolic or 155 diastolic blood pressure
• Symptomatic aortic stenosis
• Uncontrolled symptomatic heart failure
• Acute myocarditis or pericarditis
• Suspected or known dissecting aneurysm

Any adverse changes during GXT (i.e., persistent oxygen saturation drop below 88% while on prescribed oxygen therapy or significant hypotension such as mean arterial blood pressure < 60 mmHg on 2 consecutive readings within 1 minute)

High risk for non-adherence as determined by screening evaluation

Any condition, including cognitive impairment, that, in the judgment of the investigator, precludes participation because it could affect subject safety or ability of subject to complete the study

Pregnant