Project Summary/Abstract The combination of caloric restriction and exercise is the most common first-line treatment for obesity-related disorders, yet we know very little about the synergistic effects of these two very different treatments. A deeper understanding about mechanisms underlying the health benefits of adding exercise to a weight loss program is critical for optimizing modifiable components of lifestyle interventions (e.g., exercise intensity). Importantly, although a reduction in adipose tissue mass is the fundamental adaptation to weight loss, we know almost nothing about the effects that adding exercise may have on structural and functional changes within adipose tissue. This is very important because many obesity-related metabolic health complications are tightly linked with abnormalities in abdominal subcutaneous adipose tissue (aSAT). In particular, high rates of fatty acid release from aSAT, which is very common in obesity, leads to ectopic lipid deposition in liver, visceral adipose tissue, and skeletal muscle, and is a major factor underlying insulin resistance. Therefore, increasing the capacity of aSAT to store and sequester fatty acids will protect against these abnormalities. Importantly, increased capacity of aSAT to store fat does not translate to increased body fat mass, this requires an energy surplus. Based on our exciting preliminary findings, we hypothesize exercise triggers key signaling pathways in aSAT to reprogram the regulation of angiogenesis, adipogenesis, and extracellular matrix (ECM) fibrosis to remodel aSAT for more effective energy storage. We contend these exercise-induced modifications in aSAT will impart persistent health benefits even if some weight is regained after weight loss. Finally, although high-intensity interval training (HIIT) is known to induce robust cardio-metabolic improvements in adults with obesity, little known about the metabolic impact of adding HIIT to a weight loss program. Comparing HIIT vs. more “conventional” moderate-intensity continuous training (MICT) will provide important insights to optimize exercise protocols for adults with obesity. General study design: Obese adults will be randomized to: 1) MICT, 2) HIIT or 3) no exercise (NoEX) - while they all undergo a standardized calorie restricted diet until they lose 10% body weight. After losing 10% body weight, all subjects will enter a 6-month follow-up phase (no diet or exercise requirements). Because long-term adaptations to training largely stem from the accrual of responses to each exercise session, in Aim #1, we will assess changes in signaling events involved in regulating aSAT angiogenesis, adipogenesis, ECM remodeling, and inflammatory pathways, during the 24 hours after a session of exercise (HIIT and MICT). In Aim #2, we will determine the effects of adding exercise training (MICT or HIIT) to a calorie-restricted weight-loss program on changes in aSAT morphology (e.g., capillarization, ECM fibrotic content and co...