Inclusion Criteria:  'low risk' for submaximal exercise testing in accordance with the risk stratification guidelines published by the American Heart Association and the American College of Sports Medicine (AHA/ACSM criteria). We will also determine the participant's current vaccine status (influenza, chickenpox, etc) and COVID-19 infection status. Infection status will be determined via self-report and Spike protein IgG titer levels We will simply ask the participant (self-report) when they received the vaccine and, if they know, which vaccine they received (e.g. Moderna or Pfizer for the COVID-19 vaccine). However, only participants that have been vaccinated (1-3 weeks after second dose) or tested positive (greater than 2-months symptom free) for COVID-19 by either PCR, antigen, or antibody testing will be eligible for Aim 2. After providing informed consent, all participants will undergo a comprehensive screening procedure to ensure that AHA/ACSM criteria are met.  Exclusion Criteria:  Select a condition on the ACSM-AHA pre-exercise screening questionnaire indicating that physician approval is required prior to exercise Current user of tobacco products or have quit within the previous 6-months Body mass index of >30 kg/m2, or waist girth of >102cm for men and >88cm for women Use over-the-counter medication known to affect the immune system (i.e. regular use of ibuprofen/aspirin, anti-histamines or beta-blockers) chronic/debilitating arthritis Bedridden in the past three months Common illness (i.e. colds) within the past 6-weeks HIV, hepatitis, stroke, autoimmune disease, central or peripheral nervous disorders, blood vessel disease, cardiovascular disease (CVD), or use of any prescription medication Pregnant or breast-feeding; asthma, emphysema, bronchitis, kidney disease; pheochromocytoma; diabetes; overactive thyroid; history of severe anaphylactic reaction to an allergen; or are scheduled to have surgery. Individuals who pass the exclusion criteria detailed above but present with more than one of the following CVD risk factors will also be excluded from the study: family history of myocardial infarction, coronary revascularization, or sudden death before 55 years of age in father or other male first-degree relative or before 65 years of age in mother or other female first-degree relative; hypertension (systolic blood pressure of >140 mmHg or diastolic blood pressure >90 mmHg); dyslipidemia (total serum cholesterol of >200 mg/dl); pre-diabetes (fasting blood glucose of >100mg/dl but <126 mg/dl); high inflammation markers (hs-CRP>10 mg/L).