Effects of High-Intensity Interval Training Exercise in Adolescents With Hepatosteatosis

Inclusion Criteria: Initial Enrollment * Ages 13-18 years (inclusive) for both sexes * Any ethnic/racial background * English speaking competence * Teenagers ages 13-15 weighing more than 145 pounds OR teenagers ages 16-18 weighing more than 170 pounds * Low risk to participate in an exercise program as determined by "The Physical Activity Readiness Questionnaire for Everyone" * Late stages of puberty (i.e., Tanner stage IV or V) based on Tanner Staging. Inclusion Criteria: Control or Exercise Group * Presence of Non-Alcoholic Fatty Liver Disease (NAFLD) as determined by FibroScan Controlled Attenuated Parameter (CAP) score * Confirmed lack of diabetes as determined by Oral Glucose Tolerance Test (OGTT) * Confirmed eligibility per medical history Exclusion criteria: * Pre-pubertal or early stages of puberty * Pregnancy * Confirmed lack of NAFLD in the past 6 months via biopsy or MRI * Presence of an implantable medical device or metal objects in the body (a contraindication for FibroScan and/or MRI) * High-risk to participate in an exercise program as determined by "The Physical Activity Readiness Questionnaire for Everyone" * Unable to cooperate with study procedures and tests including genetic or physical conditions impacting mobility over the past year * Having known chronic illnesses/disorders that may independently affect study outcome measures: type 1 diabetes mellitus, type 2 diabetes, neurologic (e.g., epilepsy), developmental (developmental delay, autism spectrum disorder), endocrine (Cushing's, growth hormone deficiency), hepatic (other than NAFLD), autoimmune, cardiac and renal disorders * Current history of poorly-controlled asthma. * Taking any of the following medications that can affect study outcome at the time of enrollment: insulin, metformin, or any other anti-diabetics, antipsychotics, oral steroids, and anabolic drugs (growth hormone replacement therapy, testosterone, and oxandrolone). * Adolescents who have a history of claustrophobia. * Adolescents who need sedation in order to complete MRI. * Adolescents determined ineligible by the study investigator or delegated staff.