Perform structured aerobic exercise (mostly treadmill walking) of moderate-intensity for 4-5 days/week, progressing to a duration of 200 min/week. Participants will attend center-based sessions for at least 3 days/week during the first intensive 6-month phase and at least one day/week during the second 3-month transition phase (months 7-9), with recording of home-based exercise for the other 2-4 days/week.

Encouraged and taught to reduce sedentary behavior (SB) during waking hours. The SitLess treatment targets increases in postural shifts and light, spontaneous physical activity (SPA) (MET level <3).

10 item scale that assesses fatigability (fatigue in the context of a standardized task). A higher score indicates a higher performance fatigability, slower gait speed, worsening physical function.

A 10 item scale that assesses fatigability (fatigue in the context of a standardized task). Score range is 0-50 with a higher score = a higher performance fatigability, slower gait speed, worsening physical function.

A 36 item survey of overall health broken into 8 scaled scores of vitality, physical function, pain, general health, mental health, social, physical, and emotional role functioning. Ranging from 0 to 100, the lower a person scores, the more disability.

Self-reported measure used to determine a person's belief in their physical capability to successfully complete incremental walking distances (5-40 minutes) at a moderate pace. The total strength for each measure of self-efficacy is then calculated by summing the confidence ratings and dividing by the total number of items in the scale, resulting in a maximum possible efficacy score of 100.

A scale testing how satisfied an individual is with their physical fitness and abilities. Levels of satisfaction are rated on a 7 point scale from very dissatisfied to very satisfied. All items are then averaged to create a score ranging from -3 to 3.

Used to measure self-efficacy for appropriate eating using 5 subscales (Negative Emotions, Availability, Social Pressure, Physical Discomfort, Positive Activities) of 4 items each (e.g., "I can resist eating even when high-calorie foods are available"). Item responses range from 0 (not confident) to 9 (very confident). An average score is created for each subscale and then a total score by averaging across all items. On a scale from 10 to 40, higher scores represent greater confidence in being able to restrain oneself from eating under difference contexts.

Scale used to evaluate the construct of adult attachment by examining avoidance and anxiety. A person rates each statement about connection using a 7-point Likert scale which ranges from 1 (strongly disagree) to 7 (strongly agree). To obtain score, average responses from all 36 items. A score will range from 7 to 42 with a higher score representing insecure attachment.

15-item questionnaire used to assess the core characteristic of mindfulness, or an awareness of and attention to what is taking place in the present. The 15 items are collected in a Likert scale, totaled, and averaged for a final score ranging from 1-7. A higher score reflects higher levels of mindfulness and a lower score is indicative of a negative emotional state.

Scale assessing the psychological impact of living in food-abundant environments. It measures appetite for, rather than consumption of, palatable foods, at three levels of food proximity (food available, food present, and food tasted).

A questionnaire used to measure the perception of stress and how often a person felt that way in the last month. Individual scores range from 0 to 40 with higher scores indicating a person perceives higher levels of stress which could lead to or correlate with negative behaviors such as stress eating or decreases in physical activity

15-item measure of short-term changes in food cravings. Responses are made on a five-point Likert scale with response categories ranging from 1 (strongly disagree) to 5 (strongly agree). The scale yields a sum total from the five subscale scores, including, 1) an intense desire to eat; 2) anticipation of positive reinforcement that may result from eating; 3) anticipation of relief from negative states and feelings as a result of eating; 4) obsessive preoccupation with food or lack of control over eating; and 5) craving as a physiological state. Sum scores range from 15 to 90 with higher scores representing more frequent and intense experiences of craving food.

Administered during assessment visits to gain insight on the participants' opinion of the technology (i.e., Empower application and web-based questionnaires, any tests/emails received from the Empower team) used in the study. Examples of these open-ended questions include: 1) How useful did you find the Empower smartphone app?; 2) To what extent was the Empower app a burden to use?; 3) How difficult or easy was the app to use?; 4) How important did you feel the app was to your experience in the Empower study?; 5) What were one or two of your favorite and least favorite features of the Empower app? Questions were not scored or used in data analysis, but provided staff with an overall user opinion as well as constructive criticism in order to improve similar technologies in future studies.

Administered at assessment visits to gain inside on the participants' opinion on the group dynamic used in the first 6 months of the study. Examples of the dichotomous questions include: 1) Did you enjoy working with the staff and participants?; 2) Did you feel pressured by staff and or participants to do well in the study?; 3) Did you get along with the staff and participants in Empower?; 4) Did you feel comfortable expressing your ideas and opinions to staff members and fellow participants?; 5) Do you feel people a part of the Empower study care about you? Questions were not scored or used in data analysis, but provided staff with an overall opinion of participant experience as well as constructive criticism in order to improve similar group settings in future studies.

Three anthropometric measures at three anatomical locations are taken using a handheld measuring table with tension and recorded in centimeters. The waist measurement is taken at the narrowest part of the torso below the ribcage and above the umbilicus. The hip measurement is measured at the maximal circumference of the buttocks. The mid-thigh is taken with the knee bent to 90°, midway between the inguinal crease and the proximal border of the patella. The measurements taken at each site are averaged. A waist/hip ratio is calculated.

Consists of a test of balance, gait speed test, and chair stand, performed in this order. The following equipment is required for the expanded SPPB: digital stopwatch, masking tape, measuring tape, script, and a straight-backed armless chair with a hard seat. To eliminate the effect of different footwear on test performance, tests are performed in tennis shoes or comfortable walking shoes with minimal or no heels. Tests are individually scored 0-4 and then totaled for a maximal score of 12. The higher a score, the better an individual's mobility and functional ability.

Test is done on a treadmill to assess perceived fatigability at a given workload. Participants are asked to rate their RPE (rating of perceived exertion) just as they start walking (0 min, 2.0 mph), half way through (2.5 min, 2.0 mph), and at the end of the test (5 min, 2.0 mph). Heart rate via a heart rate monitoring watch will be recorded at these same intervals.

Measured during a maximal graded exercise test (GXT) to exhaustion on a treadmill using a Raise, Activate, Mobilise, Potentiate (RAMP) protocol. The GXT is used to rule out any latent coronary artery disease and to measure cardiovascular functional capacity and peak oxygen uptake. The respiratory rate, minute ventilation, breathing reserve, VO2, Validation of Carbon Dioxide Production (VCO2), respiratory exchange ratio, one metabolic equivalent (MET) level, heart rate (HR), VO2/HR, kilocalorie/minutes (Kcal/min), Rating of Perceived Exertion (RPE) and Blood pressure (BP) at test conclusion are recorded.

The Jaymar Handheld Dynamometer is used to measure grip strength in both hands. To the nearest and highest kilogram achieved, hand grip strength is a commonly used measure of upper body skeletal muscle function and has been widely used as a general indicator of frailty with predictive validity for both mortality and functional limitation.

A facemask will be placed on the participant while he/she is lying on the exam table. Measures of oxygen consumption and carbon dioxide production will be collected continuously for 30 minutes and the RMR will be calculated using the Weir equation.

Used to evaluate time spent in sedentary behavior, light, and moderate to vigorous physical activity (MVPA). An activPAL™ accelerometer (PAL Technologies, Glasgow, Scotland) is worn for 7-days at each of the three assessment visits: baseline, 6-months and 18-months. The monitor uses accelerometer-derived information about thigh position to estimate time spent in different body positions: lying or sitting = sedentary; standing still; and stepping = light and MVPA. Data is downloaded at the end of each 7-day period and cleaned and summarized for statistical analyses. The proprietary algorithm in the activPAL software is used to generate estimates of (a) Total Daily Energy Expenditure (TDEE); (b) sedentary time during the day, (c) number of breaks in sedentary time, (d) minutes spent in light activity, and (e) number of minutes spent in MVPA.

Used to determine the relationship between dynamic food variables, physical activity variables, and long-term weight loss. Prior to the start of the intervention and following the initial intervention period, participants complete week-long daily assessments. The following are the different scales and questions asked of participants: 1) Affective Valence from the Feelings Scale (scored 0 - 10 where 0 = very bad and 10 = very good). 2) Six items from the exercise-induced feelings inventory, each on a 0 ="do not feel" to 10="feel very strongly" score. Calm, peaceful, and relaxed are then averaged for a "tranquility" subscale; "fatigued, "tired" and "worn-out" are averaged for a physical exhaustion subscale. 3) Hunger was queried by "How hungry are you right now?" where 0 = not at all hungry, and 10 = very hungry. 4) An individual's craving for food was queried by "How much do you crave eating your favorite food or snack right now?" where 0 = "do not feel" and 10 = "feel very strongly".

Test is completed at a quick pace (without running) that the participant can maintain over the flat, 400 meter course. Timing begins when the participant takes his/her first step. Timing ends when the participant's whole foot crosses the line at the end of the 10th lap or the participant requests to stop. Recorded is the distance completed and time walked in minutes and seconds.

Used to determine the number of calories burned while walking at 2.0 mph on a treadmill with zero grade. Heart rate (HR) is measured continuously using a heart rate monitoring watch and will be recorded every minute. Blood pressure (BP) is monitored and recorded every minute. The test is terminated when the (HR) remains at a steady state (is within 5 beats per minute of the HR from the previous minute). The time to achieve steady state heart rate, the respiratory rate, minute ventilation, breathing reserve, VO2, VCO2, respiratory exchange ratio, MET level, HR, VO2/HR, Kcal/min, and the BP at steady state are recorded.

A visceral fat measurement is obtained through a dual-energy X-ray absorptiometry (DEXA) whole body scan in a 5-cm wide region across the entire abdomen just above the iliac crest at a level approximate with the 4th lumbar vertebrae. Mass visceral fat is measured to the nearest gram and volume to the nearest centimeter.

Hip and spine BMD is measured using specific scans of the anterior-posterior spine Lumbar vertebrae 1-Lumbar vertebrae 4 (L1-L4) and proximal femur by dual-energy X-ray absorptiometry. BMD is recorded as a t-score with a lower score indicative of less bone density and increased risk for osteoporosis.

An 8-hour fasting venous blood sample is collected to measure cardiometabolic changes lipoprotein lipids, C-reactive protein, HbA1c, glucose and insulin.

Scale used to test how satisfied participants are with their physical fitness, functional ability, and physical appearance. Participants rate their level of satisfaction on a 7-point scale from very dissatisfied to very satisfied. Average all items to create a score ranging from -3 to 3. Higher values represent greater satisfaction with physical function and importance.

Weight loss: All participants will undergo a dietary WL intervention designed to elicit behavioral changes leading to decreased caloric intake sufficient to yield a ~10% loss of initial body mass. The WL intervention includes nutrition education, state-of-the-art behavioral methods for promoting WL, and strategies that optimize self-regulation.

Sitless: Encouraged and taught to reduce sedentary behavior (SB) during waking hours. The SitLess treatment targets increases in postural shifts and light, spontaneous physical activity (SPA) (MET level <3).

Weight loss: All participants will undergo a dietary WL intervention designed to elicit behavioral changes leading to decreased caloric intake sufficient to yield a ~10% loss of initial body mass. The WL intervention includes nutrition education, state-of-the-art behavioral methods for promoting WL, and strategies that optimize self-regulation.

Exercise: Perform structured aerobic exercise (mostly treadmill walking) of moderate-intensity for 4-5 days/week, progressing to a duration of 200 min/week. Participants will attend center-based sessions for at least 3 days/week during the first intensive 6-month phase and at least one day/week during the second 3-month transition phase (months 7-9), with recording of home-based exercise for the other 2-4 days/week.

Total of all reporting groups

Montreal Cognitive Assessment (MoCA) is to help determine if impaired cognition would preclude them from participating. The test is administered in approximately 10 minutes and it assesses several cognitive domains. Scores range from 0 to 30, with a lower score indicating cognitive impairment.

Center for Epidemiological Studies-Depression (CES-D) is administered to help exclude potential participants with clinically significant depression. The CES-D is a 20-item tool that asks subjects to rate how often over the past week they experienced symptoms associated with depression. Scores range from 0 to 60, with high scores indicating greater depressive symptoms. A cutoff score of 16 or greater is indicative of clinical depression.

A score is calculated by dividing waist circumference by hip circumference. High risk for men is a score greater than or equal to 0.95 and greater than or equal to 0.86 for women.

The SPPB consists of a test of balance, gait speed test, and chair stand, performed in this order to measure lower-extremity function. A score is totaled and can equal 0 to 12 with a lower score indicating poorer mobility and physical function.

Consists of a test of balance, gait speed test, and chair stand, performed in this order. The following equipment is required for the expanded SPPB: digital stopwatch, masking tape, measuring tape, script, and a straight-backed armless chair with a hard seat. To eliminate the effect of different footwear on test performance, tests are performed in tennis shoes or comfortable walking shoes with minimal or no heels. Tests are individually scored 0-4 and then totaled for a maximal score of 12. The higher a score, the better an individual's mobility and functional ability.

Measured during a maximal graded exercise test (GXT) to exhaustion on a treadmill using a RAMP protocol. The GXT is used to rule out any latent coronary artery disease and to measure cardiovascular functional capacity and peak oxygen uptake. The speed is set at the fastest speed that the participant can maintain for several minutes, and the grade steadily increases until the test is stopped. The respiratory rate, minute ventilation, breathing reserve, VO2, VCO2, respiratory exchange ratio, MET level, HR, VO2/HR, Kcal/min, RPE and BP at test conclusion are recorded.

Weight loss: All participants will undergo a dietary WL intervention designed to elicit behavioral changes leading to decreased caloric intake sufficient to yield a ~10% loss of initial body mass. The WL intervention includes nutrition education, state-of-the-art behavioral methods for promoting WL, and strategies that optimize self-regulation.

Exercise: Perform structured aerobic exercise (mostly treadmill walking) of moderate-intensity for 4-5 days/week, progressing to a duration of 200 min/week. Participants will attend center-based sessions for at least 3 days/week during the first intensive 6-month phase and at least one day/week during the second 3-month transition phase (months 7-9), with recording of home-based exercise for the other 2-4 days/week.

Weight loss: All participants will undergo a dietary WL intervention designed to elicit behavioral changes leading to decreased caloric intake sufficient to yield a ~10% loss of initial body mass. The WL intervention includes nutrition education, state-of-the-art behavioral methods for promoting WL, and strategies that optimize self-regulation.

Sitless: Encouraged and taught to reduce sedentary behavior (SB) during waking hours. The SitLess treatment targets increases in postural shifts and light, spontaneous physical activity (SPA) (MET level <3).

Measured in clinic on the same scale

The CONSORT represents all 6 waves while our results only include data for Waves 1-4 due to COVID restrictions impacting the 18mo visit data for Waves 5 and 6.

Measured in clinic on the same scale

The CONSORT represents all 6 waves while our results only include data for Waves 1-4 due to COVID restrictions impacting the 18mo visit data for Waves 5 and 6.

13 item scale used to measure fatigue over the past week with a 4-point Likert scale. The score range is 0-52 with a score of less than 30 indicating severe fatigue, and higher score denoting a better quality of life.

DAn 8 item questionnaire that assess fatigue over the past 7 days. All items are summed with the lowest possible score equaling 8 and the highest, a 40. A higher score indicates more fatigue.

10 item scale that assesses fatigability (fatigue in the context of a standardized task). A higher score indicates a higher performance fatigability, slower gait speed, worsening physical function.

A 10 item scale that assesses fatigability (fatigue in the context of a standardized task). Score range is 0-50 with a higher score = a higher performance fatigability, slower gait speed, worsening physical function.

A 36 item survey of overall health broken into 8 scaled scores of vitality, physical function, pain, general health, mental health, social, physical, and emotional role functioning. Ranging from 0 to 100, the lower a person scores, the more disability.

Self-reported measure used to determine a person's belief in their physical capability to successfully complete incremental walking distances (5-40 minutes) at a moderate pace. The total strength for each measure of self-efficacy is then calculated by summing the confidence ratings and dividing by the total number of items in the scale, resulting in a maximum possible efficacy score of 100.

A scale testing how satisfied an individual is with their physical fitness and abilities. Levels of satisfaction are rated on a 7 point scale from very dissatisfied to very satisfied. All items are then averaged to create a score ranging from -3 to 3.

Used to measure self-efficacy for appropriate eating using 5 subscales (Negative Emotions, Availability, Social Pressure, Physical Discomfort, Positive Activities) of 4 items each (e.g., "I can resist eating even when high-calorie foods are available"). Item responses range from 0 (not confident) to 9 (very confident). An average score is created for each subscale and then a total score by averaging across all items. On a scale from 10 to 40, higher scores represent greater confidence in being able to restrain oneself from eating under difference contexts.

Scale used to evaluate the construct of adult attachment by examining avoidance and anxiety. A person rates each statement about connection using a 7-point Likert scale which ranges from 1 (strongly disagree) to 7 (strongly agree). To obtain score, average responses from all 36 items. A score will range from 7 to 42 with a higher score representing insecure attachment.

15-item questionnaire used to assess the core characteristic of mindfulness, or an awareness of and attention to what is taking place in the present. The 15 items are collected in a Likert scale, totaled, and averaged for a final score ranging from 1-7. A higher score reflects higher levels of mindfulness and a lower score is indicative of a negative emotional state.

Scale assessing the psychological impact of living in food-abundant environments. It measures appetite for, rather than consumption of, palatable foods, at three levels of food proximity (food available, food present, and food tasted).

A questionnaire used to measure the perception of stress and how often a person felt that way in the last month. Individual scores range from 0 to 40 with higher scores indicating a person perceives higher levels of stress which could lead to or correlate with negative behaviors such as stress eating or decreases in physical activity

15-item measure of short-term changes in food cravings. Responses are made on a five-point Likert scale with response categories ranging from 1 (strongly disagree) to 5 (strongly agree). The scale yields a sum total from the five subscale scores, including, 1) an intense desire to eat; 2) anticipation of positive reinforcement that may result from eating; 3) anticipation of relief from negative states and feelings as a result of eating; 4) obsessive preoccupation with food or lack of control over eating; and 5) craving as a physiological state. Sum scores range from 15 to 90 with higher scores representing more frequent and intense experiences of craving food.

Administered during assessment visits to gain insight on the participants' opinion of the technology (i.e., Empower application and web-based questionnaires, any tests/emails received from the Empower team) used in the study. Examples of these open-ended questions include: 1) How useful did you find the Empower smartphone app?; 2) To what extent was the Empower app a burden to use?; 3) How difficult or easy was the app to use?; 4) How important did you feel the app was to your experience in the Empower study?; 5) What were one or two of your favorite and least favorite features of the Empower app? Questions were not scored or used in data analysis, but provided staff with an overall user opinion as well as constructive criticism in order to improve similar technologies in future studies.

Administered at assessment visits to gain inside on the participants' opinion on the group dynamic used in the first 6 months of the study. Examples of the dichotomous questions include: 1) Did you enjoy working with the staff and participants?; 2) Did you feel pressured by staff and or participants to do well in the study?; 3) Did you get along with the staff and participants in Empower?; 4) Did you feel comfortable expressing your ideas and opinions to staff members and fellow participants?; 5) Do you feel people a part of the Empower study care about you? Questions were not scored or used in data analysis, but provided staff with an overall opinion of participant experience as well as constructive criticism in order to improve similar group settings in future studies.

Three anthropometric measures at three anatomical locations are taken using a handheld measuring table with tension and recorded in centimeters. The waist measurement is taken at the narrowest part of the torso below the ribcage and above the umbilicus. The hip measurement is measured at the maximal circumference of the buttocks. The mid-thigh is taken with the knee bent to 90°, midway between the inguinal crease and the proximal border of the patella. The measurements taken at each site are averaged. A waist/hip ratio is calculated.

Consists of a test of balance, gait speed test, and chair stand, performed in this order. The following equipment is required for the expanded SPPB: digital stopwatch, masking tape, measuring tape, script, and a straight-backed armless chair with a hard seat. To eliminate the effect of different footwear on test performance, tests are performed in tennis shoes or comfortable walking shoes with minimal or no heels. Tests are individually scored 0-4 and then totaled for a maximal score of 12. The higher a score, the better an individual's mobility and functional ability.

Test is done on a treadmill to assess perceived fatigability at a given workload. Participants are asked to rate their RPE (rating of perceived exertion) just as they start walking (0 min, 2.0 mph), half way through (2.5 min, 2.0 mph), and at the end of the test (5 min, 2.0 mph). Heart rate via a heart rate monitoring watch will be recorded at these same intervals.

Measured during a maximal graded exercise test (GXT) to exhaustion on a treadmill using a Raise, Activate, Mobilise, Potentiate (RAMP) protocol. The GXT is used to rule out any latent coronary artery disease and to measure cardiovascular functional capacity and peak oxygen uptake. The respiratory rate, minute ventilation, breathing reserve, VO2, Validation of Carbon Dioxide Production (VCO2), respiratory exchange ratio, one metabolic equivalent (MET) level, heart rate (HR), VO2/HR, kilocalorie/minutes (Kcal/min), Rating of Perceived Exertion (RPE) and Blood pressure (BP) at test conclusion are recorded.

The Jaymar Handheld Dynamometer is used to measure grip strength in both hands. To the nearest and highest kilogram achieved, hand grip strength is a commonly used measure of upper body skeletal muscle function and has been widely used as a general indicator of frailty with predictive validity for both mortality and functional limitation.

A facemask will be placed on the participant while he/she is lying on the exam table. Measures of oxygen consumption and carbon dioxide production will be collected continuously for 30 minutes and the RMR will be calculated using the Weir equation.

Used to evaluate time spent in sedentary behavior, light, and moderate to vigorous physical activity (MVPA). An activPAL™ accelerometer (PAL Technologies, Glasgow, Scotland) is worn for 7-days at each of the three assessment visits: baseline, 6-months and 18-months. The monitor uses accelerometer-derived information about thigh position to estimate time spent in different body positions: lying or sitting = sedentary; standing still; and stepping = light and MVPA. Data is downloaded at the end of each 7-day period and cleaned and summarized for statistical analyses. The proprietary algorithm in the activPAL software is used to generate estimates of (a) Total Daily Energy Expenditure (TDEE); (b) sedentary time during the day, (c) number of breaks in sedentary time, (d) minutes spent in light activity, and (e) number of minutes spent in MVPA.

Used to determine the relationship between dynamic food variables, physical activity variables, and long-term weight loss. Prior to the start of the intervention and following the initial intervention period, participants complete week-long daily assessments. The following are the different scales and questions asked of participants: 1) Affective Valence from the Feelings Scale (scored 0 - 10 where 0 = very bad and 10 = very good). 2) Six items from the exercise-induced feelings inventory, each on a 0 ="do not feel" to 10="feel very strongly" score. Calm, peaceful, and relaxed are then averaged for a "tranquility" subscale; "fatigued, "tired" and "worn-out" are averaged for a physical exhaustion subscale. 3) Hunger was queried by "How hungry are you right now?" where 0 = not at all hungry, and 10 = very hungry. 4) An individual's craving for food was queried by "How much do you crave eating your favorite food or snack right now?" where 0 = "do not feel" and 10 = "feel very strongly".

Test is completed at a quick pace (without running) that the participant can maintain over the flat, 400 meter course. Timing begins when the participant takes his/her first step. Timing ends when the participant's whole foot crosses the line at the end of the 10th lap or the participant requests to stop. Recorded is the distance completed and time walked in minutes and seconds.

Used to determine the number of calories burned while walking at 2.0 mph on a treadmill with zero grade. Heart rate (HR) is measured continuously using a heart rate monitoring watch and will be recorded every minute. Blood pressure (BP) is monitored and recorded every minute. The test is terminated when the (HR) remains at a steady state (is within 5 beats per minute of the HR from the previous minute). The time to achieve steady state heart rate, the respiratory rate, minute ventilation, breathing reserve, VO2, VCO2, respiratory exchange ratio, MET level, HR, VO2/HR, Kcal/min, and the BP at steady state are recorded.

A visceral fat measurement is obtained through a dual-energy X-ray absorptiometry (DEXA) whole body scan in a 5-cm wide region across the entire abdomen just above the iliac crest at a level approximate with the 4th lumbar vertebrae. Mass visceral fat is measured to the nearest gram and volume to the nearest centimeter.

Hip and spine BMD is measured using specific scans of the anterior-posterior spine Lumbar vertebrae 1-Lumbar vertebrae 4 (L1-L4) and proximal femur by dual-energy X-ray absorptiometry. BMD is recorded as a t-score with a lower score indicative of less bone density and increased risk for osteoporosis.

An 8-hour fasting venous blood sample is collected to measure cardiometabolic changes lipoprotein lipids, C-reactive protein, HbA1c, glucose and insulin.

Scale used to test how satisfied participants are with their physical fitness, functional ability, and physical appearance. Participants rate their level of satisfaction on a 7-point scale from very dissatisfied to very satisfied. Average all items to create a score ranging from -3 to 3. Higher values represent greater satisfaction with physical function and importance.

Weight loss: All participants will undergo a dietary WL intervention designed to elicit behavioral changes leading to decreased caloric intake sufficient to yield a ~10% loss of initial body mass. The WL intervention includes nutrition education, state-of-the-art behavioral methods for promoting WL, and strategies that optimize self-regulation.

Sitless: Encouraged and taught to reduce sedentary behavior (SB) during waking hours. The SitLess treatment targets increases in postural shifts and light, spontaneous physical activity (SPA) (MET level <3).

Weight loss: All participants will undergo a dietary WL intervention designed to elicit behavioral changes leading to decreased caloric intake sufficient to yield a ~10% loss of initial body mass. The WL intervention includes nutrition education, state-of-the-art behavioral methods for promoting WL, and strategies that optimize self-regulation.

Exercise: Perform structured aerobic exercise (mostly treadmill walking) of moderate-intensity for 4-5 days/week, progressing to a duration of 200 min/week. Participants will attend center-based sessions for at least 3 days/week during the first intensive 6-month phase and at least one day/week during the second 3-month transition phase (months 7-9), with recording of home-based exercise for the other 2-4 days/week.