Inclusion Criteria:  ICU admission and subsequent discharge for primary diagnosis of COVID-19 respiratory failure or infection requiring intubation and mechanical ventilation for ≥ 48 hours with an ICU length of stay of ≥ 4 days. Expected to be discharged directly home from the hospital (not to a skilled nursing facility, inpatient rehabilitation center, or long-term acute care hospital) Able to ambulate with or without a gait aid prior to hospital discharge Age ≥ 18 years  Exclusion Criteria:  Not ambulating independently prior to COVID-19 illness (use of a gait aid permitted) Functional impairment resulting in inability to exercise at hospital discharge (including need for home oxygen requirement) 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 screening 6MST (i.e., oxygen saturation drop below 88-90% 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 Anticipated hospital discharge before baseline study measures could be completed 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