Inclusion Criteria:  Typically developing youth. Overweight/obese (BMI >= 85th percentile) Does not meet current PA guidelines Able and willing to complete HIIT exercise intervention. Space for a stationary bike in the residence.  Exclusion Criteria:  Diagnoses of neurodevelopment or psychiatric disorders. Diabetes, cardiovascular, pulmonary, or other significant medical problems. Taking medications know to alter metabolism. Allergy to metals. Inability to participate in HIIT-based exercise or active involvement in sports/exercise programs. Pregnancy.