Participants will be asked to report their current level of commitment to the 16-week program and attending their next exercise session via a visual analogue scale anchored with "0" (0% committed) to "100" (100% committed). They subsequently responded to free-text questions related to what they needed to do or what the research team could do to increase their level of commitment. Next, they answered the question "Will you attend your next RET session?" (yes/no response buttons), and then provided an electronic signature confirming they would attend.

The GRID-HAM-D is a clinician-completed questionnaire that will be used to rate depressive symptom severity. The questionnaire is designed for adults and is used to rate the intensity and frequency of depressive symptoms by probing mood, feelings of guilt, suicidal ideation, insomnia, agitation or retardation, anxiety, weight loss, and somatic symptoms. Clinical Interviewers will follow the Structured Interview Guide and use GRID scoring, in which dimensions of intensity and frequency of a symptom are rated independently for each item. Higher scores reflect greater symptom severity, categorized as Normal (0-7), Mild Depression (8-13), Moderate Depression (14-18), Severe Depression (19-22), and Very Severe Depression (>23).

This is a clinician-administered semi-structured interview guide for making diagnoses according to the diagnostic criteria published in the American Psychiatric Association's Diagnostic and Statistical Manual for Mental Disorders (DSM-5). It provides diagnoses for depressive and bipolar disorders, schizophrenia spectrum and other psychotic disorders, substance use disorders, anxiety disorders (panic disorder, agoraphobia, social anxiety disorder, generalized anxiety disorder), obsessive-compulsive disorder, posttraumatic stress disorder, attention-deficit/hyperactivity disorder, and adjustment disorder. The SCID will be administered by a Clinical Interviewer to diagnose Major Depressive Disorder and assess for exclusion criteria in this study.

This is a self-administered 16-item questionnaire that assesses the severity of nine depressive symptoms in the last 7 days. Each item is rated on a 4-point scale (0-3), with total scores ranging from 0-27. Higher scores indicate more severe depression.

Middle Cerebral Artery (MCA) blood flow velocity will be measured under supine, resting conditions using non-invasive techniques following 10 min of quiet rest in a dimly lit room. It will be assessed in duplicate and averaged for analyses. Measurements will be taken from the left middle cerebral artery (MCA) following standardized, recommended insonation protocols using a 2-MHz Transcranial Doppler (TCD) probe secured to the temporal window via a headset. MCA mean blood velocity will be calculated using a standard algorithm implemented on the device, averaged over a 60-sec epoch.

Middle Cerebral Artery (MCA) blood flow pulsatility will be measured under supine, resting conditions using non-invasive techniques following 10 min of quiet rest in a dimly lit room. It will be assessed in duplicate and averaged for analyses. Measurements will be taken from the left middle cerebral artery (MCA) following standardized, recommended insonation protocols using a 2-MHz Transcranial Doppler (TCD) probe secured to the temporal window via a headset. Cerebral pulsatility will be quantified using the pulsatility index, calculated as (systolic -diastolic velocity)/mean velocity using TCD, averaged over a 60-sec epoch.

A 5-RM testing method will be used to calculate each participant's estimated 1-RM, in which participants will lift the maximum amount of weight that can be lifted five times with correct form, timing, and breathing. Maximum strength will be assessed on one upper body (chest press) and one lower body (leg press) major muscle group, completed using the Keiser resistance machines.

A research assistant will ask the participant to sit in a chair and rest his/her arm on the table with the elbow on top of a mouse pad and arm held at a right angle to adjust the dynamometer to the participant's hand size. The participant will then squeeze the dynamometer twice to practice. To begin the assessment, the participant will use his/her right hand and squeeze as hard as possible. Three trials will be attempted with each hand. When the right hand is complete, the left hand will be assessed (i.e., 3 trials). A sum of the greatest effort (number) for each hand is totaled (rounded to the nearest 2 kilograms) and will be recorded.

Aortic stiffness will be assessed via carotid-femoral pulse wave velocity (CfPWV). Carotid and femoral pressure waveforms will be captured with applanation tonometry and simultaneous R-wave gating. CfPWV will be calculated as the distance between carotid and femoral sites divided by the time lag (Δt) between carotid-femoral waves.

The carotid structure will be assessed by measuring diameter, wall thickness, and stiffness using ultrasound and carotid pressures obtained from contralateral carotid tonometry during CfPWV assessment. WV-β will be calculated using onboard wall-tracking software to determine common carotid stiffness and diameter. Carotid wall thickness (IMT) will be measured using semi-automated calipers.

The International Physical Activity Questionnaire Short Form (IPAQ-SF) is a measure that assesses the types of the intensity of physical activity and sitting time that people did over the past 7 days using seven questions via self-report by the participant. Participants are instructed to report the number of days per week and minutes per day they spend engaging in 1) vigorous activity, 2) moderate activity, 3) walking, and 4) sitting. Responses are used to calculate total minutes of walking, minutes of moderate-to-vigorous physical activity per week, and hours of sitting time on a weekday and weekend day, with higher scores indicating greater levels of each behavior.

Participants will place an activPAL on the midline of the thigh on either leg and wear the monitor 24 hours per day, removing it only for water-based activities (e.g., swimming). For data to be valid, the monitor must have been worn for 20 hours on at least 4 days, including a minimum of 3 weekdays and 1 weekend day. Sleep time will be parsed out from each day's sitting/lying time automatically using PALanalysis. From these data, average minutes of sitting per day will be used to assess total sedentary time, minutes of stepping time with a cadence ≥75 and <100 will be used to assess minutes of light intensity physical activity, and minutes of stepping time with a cadence ≥100 will be used to assess minutes of moderate to vigorous physical activity (MVPA).

The SF-36 assesses health-related qualify of life. It consists of eight scaled scores (including vitality, physical functioning, bodily pain, general health perceptions, physical role functioning, emotional role functioning, social role functioning, and mental health), which are the weighted sums of the questions in their section. Each scale is directly transformed into a 0-100 scale on the assumption that each question carries equal weight. The lower the score the more disability. The higher the score the less disability (i.e., a score of zero is equivalent to maximum disability and a score of 100 is equivalent to no disability).

The Penn State Worry Questionnaire (PSWQ) is a 16-item questionnaire that assesses the trait of worry, using Likert rating from 1 (not at all typical of me) to 5 (very typical of me). The total scores range from 16 to 80 with higher scores indicating greater levels of worry.

This is a 10-item questionnaire to measure an individual's level of perceived stress in the past month. The response options for each feeling or thought indicate the frequency with which it occurred: 0 = Never; 1 = Almost Never; 2 = Sometimes; 3 = Fairly Often; 4 = Very Often.

The EIS is a 9-item questionnaire used to assess the salience of identifying with exercise as an integral portion of the self-concept. Participants respond to each EIS item on a scale, anchored by (1) Strongly Disagree and (7) Strongly Agree, after reading a stem that contextualized each item within their personal exercise experiences (e.g., "The following questions concern your personal beliefs about exercise. Please indicate the degree to which you agree or disagree with each statement when thinking about your exercise participation."). Higher scores reflect greater feelings of exercise as an integral part of their self-identity.