Some military personnel who have been exposed to burn pit emissions, desert dust, and other airborne hazards experience new respiratory symptoms after deployment. The goal of this clinical trial is to learn about exercise in veterans with new respiratory symptoms after deployment to Southwest Asia. The main questions it aims to answer are:

1. Do veterans with new respiratory symptoms after deployment have heart or lung abnormalities that contribute to difficulty exercising?
2. Does high-intensity interval training (HIIT) improve fitness and symptoms?

Study participants will complete the following:

1. Study Visits 1A and 1B: Exercise test (VO2max test), echocardiogram (heart ultrasound), blood tests, questionnaires
2. Exercise program: 12 weeks of 3x/week supervised HIIT on upright stationary bicycle (~40 minutes each) and 3x/week home aerobic exercise (45 minutes each)
3. Study Visits 2A and 2B: Exercise test (VO2max test), echocardiogram (heart ultrasound), blood tests, questionnaires

Inclusion Criteria:

• Deployment of ≥30 days to Iraq, Afghanistan, Kuwait, Saudi Arabia, Bahrain, Qatar, United Arab Emirates, Kyrgyzstan, or Djibouti after September 2001
• New onset of cough, shortness of breath, chest tightness/wheezing, dyspnea on exertion or exercise intolerance which started during or after deployment
• Definite or probable distal lung disease (≥1 hyperinflation, emphysema, bronchiolitis, small airways inflammation, peribronchiolar fibrosis, or granulomatous pneumonitis on surgical lung biopsy; or ≥2 centrilobular nodularity, air trapping, mosaicism, or bronchial wall thickening on chest computed tomography [CT]), definite or probable deployment-related asthma (≥1 increase in post-bronchodilator forced expiratory volume in 1 second [FEV1] ≥12% and ≥200cc, or methacholine challenge with provocation concentration causing a 20% decline in FEV1 [PC20] ≤16 mg/mL), or unexplained dyspnea on exertion or exercise intolerance despite noninvasive testing including pulmonary function testing, methacholine challenge, transthoracic echocardiography, and/or chest computed tomography
• Current symptoms of dyspnea on exertion or exercise intolerance
• Residence <90 miles from Rocky Mountain Regional VA and ability / willingness to attend in-person HIIT sessions and research visits
• Vaccinated against Coronavirus-19 including primary series and (if eligible) ≥1 booster

Exclusion Criteria:

• Active / uncontrolled cardiovascular or pulmonary disease (e.g. hypertension with blood pressure >160/100 despite antihypertensive therapy, known hypertensive response to exercise [systolic blood pressure >220 mmHg in men / >190 mmHg in women], coronary artery disease, left ventricular ejection fraction ≤45% or heart failure with preserved ejection fraction with ongoing symptoms despite diuretic therapy, uncontrolled arrhythmia, moderate or severe valvular abnormality, diabetes with HbA1c >8.5%, asthma exacerbation requiring steroids within 4 weeks of enrollment, interstitial lung disease, untreated severe obstructive sleep apnea)
• Pre-deployment history of cardiovascular or pulmonary disease including coronary artery disease, left ventricular ejection fraction ≤45% or heart failure with preserved ejection fraction requiring diuretic therapy, arrhythmia, valvular abnormality, chronic obstructive pulmonary disease, asthma (excluding childhood asthma that did not persist into adulthood), interstitial lung disease, or pulmonary hypertension
• Body mass index <18.5 or >45
• Anemia with hemoglobin <10 g/dl
• Disorders that adversely influence exercise ability (e.g. arthritis or peripheral vascular disease)
• Current fitness program (e.g. >30 minutes at metabolic equivalents [METs] >6 3 times/week or more)
• Pregnancy or possible anticipated pregnancy during study duration
• Post-menopausal status in women

From enrollment until end of follow-up, up to 4 months