The term "Overlap Syndrome" (OS) is used to describe the presence of both chronic obstructive pulmonary disease (COPD) and obstructive sleep apnea (OSA) in a single patient. Due to premature aging, patients with OS are prone to developing functional decline up to 20 years earlier than the general population. The International Classification of Functioning, Disability and Health (ICF) evaluates functional status in chronic pulmonary disease globally in 5 domains. We propose to study validated outcomes in 3 of these domains: 1) participation in life situations, measured by the 36-item Short Form Survey (SF-36); 2) physical activity (PA), measured by daily step counts; and 3) cardiovascular health, measured by cardiorespiratory fitness (CRF), flow-mediated endothelial dilation (FMD) and serum hs-CRP, lipids and glucose. Our long-term goal is to develop an exercise strategy tailored to Veterans with OS which will reduce their risk of functional decline through increased PA. Excessive daytime sleepiness (EDS) is a common symptom of OSA that persists in a third of patients despite optimal treatment with continuous positive airway pressure (CPAP). EDS is associated with decreased quality of life and daily activity and increased risk of CVD and further, improves with exercise. Understanding the relationship of EDS with these domains of functional status within the context of an exercise intervention provides an opportunity to tailor exercise strategies to this complex patient population. We propose to investigate Veterans with EDS-OS because they are at highest risk for functional decline yet have the greatest barriers to exercise. Exercise trials performed in patients with COPD or OSA show that moderate intensity continuous training (MICT) decreased EDS and increased SF-36, PA, CRF and hs-CRP. MICT remains underutilized despite its well-established benefits. Thus, we propose to test moderate intensity interval training (MIIT), a novel 5-minute interval-based exercise intervention that meets the individual needs and capacities of Veterans with OS. In addition, we will study behavioral barriers to exercise using the self-efficacy for exercise (SEE) Scale and Brainwriting Premortem, an efficient stakeholder feedback technique, to facilitate the design of a future home- based MIIT intervention and its successful translation into bouts of daily PA (future Merit Application). We propose a randomized trial of MIIT (5-minute intervals at 50% VO2peak 3 times weekly for 12 weeks) in Veterans with OS vs. standard of care controls. The Epworth Sleepiness Scale (ESS) will be assessed at baseline. Veterans with the EDS-OS phenotype (ESS >10) will enter the MIIT trial. The specific aims are: 1) To determine the effect of MIIT on participation in life situations compared to usual care control Hypothesis 1: MIIT improves: a) SF-36 physical and mental scores; and b) Epworth Sleepiness Scale. Hypothesis 2. The EDS-OS phenotype will be associated with poor SF-36 scores ...