RESISTance Exercise for Depression Trial

Inclusion Criteria: * Be diagnosed with DSM-5 MDD, confirmed via Structured Clinical Interview for DSM-5 (SCID). * Have current depressive symptoms of at least mild severity defined by the Hamilton Rating Scale of Depression 17 greater than or equal to 8 (HAMD; using the GRID-HAMD evaluated by trained, masked raters) * Be ages 18-65 * EITHER not taking any mental health medications or seeking other mental health treatment (e.g., behavioral, psychological) OR be on a stable mental health medication and/or treatment regimen for the past 8 weeks, and intend to maintain that regimen for the duration of the study * Safe to exercise based on physical activity screening questions or physician clearance * Willing to be randomized to either condition * have a Smartphone Exclusion Criteria: * Currently pregnant, nursing, or planning to become pregnant during the trial * Class III+ obesity * Diagnosed with lifetime or current Psychosis, Mania, or Bipolar Disorder, via the SCID * Diagnosed with current Substance Use Disorder, via the SCID * Active suicidal ideation with specific plan and intent ('5' score on Suicidal Ideation from Columbia Suicide Severity Rating Scale), which would necessitate immediate emergent care * Exhibit behavioral disturbance (e.g., aggression, mild-moderate cognitive impairment) that would significantly interfere with study participation, as assessed by clinical research personnel * Currently meets resistance exercise recommendations (2 days per week) for the last 8 weeks * Self-reporting a concussion/traumatic brain injury within the last 3 months * Having cardiovascular disease, uncontrolled hypertension, or uncontrolled diabetes