Participants in the control group will be administered writing prompts in the same format and frequency as the values intervention, but with prompts focused on self-reflection related to physical activity.

The "Amotivation" subscale of the BREQ-3 refers to a non-self-determined form of regulation, where there is no intention at all to engage in exercise. A sample item is "I don't see why I should have to exercise."

The "External Regulation" subscale of the BREQ-3 refers to motivation that is externally regulated by compliance, conformity, or external rewards and punishment and that is not self-determined. A sample item is "I exercise because other people say I should."

The "Introjected Regulation" subscale of the BREQ-3 refers to motivation that is driven by self-control, an effort to maintain self-esteem, and/or internal rewards and punishments. A sample item is "I feel guilty when I don't exercise."

The "Identified Regulation" subscale of the BREQ-3 refers to motivation that is based on the conscious acceptance of exercise as a personal value that overrides any difficulties or obstacles in its way. A sample item is "I think it is important to make the effort to exercise regularly."

The "Integrated Regulation" subscale of the BREQ-3 refers to motivation to exercise that is fully congruent with one's identity. Integrated Regulation is fully self-determined since it is engaged in willingly. However, it is distinguished from intrinsic motivation because the reason behind engaging in the behavior (i.e., exercise) is still for separable outcomes and not for the sake of itself. A sample item is "I exercise because it is consistent with my life goals."

The "Intrinsic Regulation" subscale of the BREQ-3 refers to motivation to exercise that is entirely motivated by interest and enjoyment inherent in exercise itself. It is fully self-motivated and self-determined. A sample item is "I get pleasure and satisfaction from participating in exercise."

A self-report scale that measures an individual's general mental, physical, and social health. This scale consists of 10 items, 9 of which are rated on a scale from 1 (poor) to 5 (excellent), and 1 item pertaining to pain that is rated on a scale from 0 (no pain) to 10 (worst pain imaginable). Overall, higher scores indicate better global health. Scores can be calculated using either the HealthMeasures Scoring Service, which uses response pattern scoring, or by using the manual to convert raw scores to t-scores.

The "Global Mental Health" subscale of the PROMIS Global Health questionnaire v1.2 provides a generic self-assessment of one's mental health. A sample item is "In general, how would you rate your mental health, including your mood and ability to think?"

The "Global Physical Health" subscale of the PROMIS Global Health questionnaire v1.2 provides a generic self-assessment of one's physical health. A sample item is "In general, how would you rate your physical health?"

A self-report scale that measures satisfaction with performing one's usual social roles and activities. The scale consists of 8 items that are rated on a scale from 1 (not at all) to 5 (very much). Scores can be calculated using either the Assessment Center Scoring Service, which uses response pattern scoring, or by using the manual to convert raw scores to t-scores. Higher scores indicate better satisfaction with one's social role and activities.

A self-report scale that measures psychological flexibility and psychological inflexibility. The scale consists of 24 items, and participants are asked to consider the past two weeks and select a response from a scale ranging from "Never True" to "ALWAYS True". A global score on psychological flexibility and inflexibility is produced, in addition to subscale scores pertaining to each of the six dimensions of psychological flexibility and inflexibility. Scores range from a minimum of 1.0 to 6.0, with higher scores reflecting higher levels of the domain being assessed (i.e., psychological flexibility or inflexibility, etc.).

The "Contact With Values" subscale of the MPFI-24 falls under the psychological flexibility factor and measures the extent to which an individual is connected to what is important to them in life, giving direction to their actions. Participants are asked to consider the past two weeks when rating their responses, and a sample item is: "I was very in-touch with what is important to me and my life."

The "Lack of Contact With Values" subscale of the MPFI-24 falls under the psychological inflexibility factor and measures the extent to which an individual is disconnected from their values in their daily life. Participants are asked to consider the past two weeks when rating their responses, and a sample item is: "When life got hectic, I often lost touch with the things I value."

A self-report scale that measures how well respondents understand and can articulate their values. The VCQ consists of 7 items rated on a scale from 1 (strongly disagree) to 5 (strongly agree). Total scores range from a minimum of 7 to a maximum of 35, with higher scores indicating higher levels of clarity, understanding, and articulation of one's own values.

A self-report scale that measures global self-compassion across six factors: self-kindness, self-judgment, common humanity, isolation, and mindfulness. The SCS-SF consists of 12 items rated on a scale from 1 (almost never) to 5 (almost always). Total scores range from a minimum of 1.0 to a maximum of 5.0, with higher scores indicating greater levels of self-compassion.

Participants will be asked to choose one of the following statements that best describe their participation in the survey, noting that their answer does not impact their participation in the study in any way: "I answered every question carefully and honestly" (1); "I answered most questions carefully and honestly" (2); "I randomly responded and/or did not respond honestly to about half of the questions" (3); "I randomly responded and/or did not respond honestly to most questions" (4); and "I randomly responded and/or did not respond honestly to any questions" (5). Participants who score a 4 or 5 will be screened out for random responding.

A self-report measure of the perceived credibility of and expectations toward a treatment. The CEQ consists of 6 items, 3 for Credibility and 3 for Expectancy. An average score ranging from 1 to 9 will be calculated for Credibility, with higher scores a greater perception of the intervention's credibility by the participants. For the expectancy component, an average percentage score will be calculated ranging from 0% to 100%, with higher percentages indicating more positive expectations towards the treatment.

A self-report measure of usability of a technological system. The SUS consists of 10 items rated on a scale from 1 (strongly disagree) to 5 (strongly agree). Scores are summed and doubled such that they range from 0 to 100 (as per the official scoring instructions), with high scores indicating greater usability.

A self-report measure of treatment acceptability. The TEI-SF consists of 7 items rated from 1 (strongly disagree) to 5 (strongly agree). Scores range from 7 to 35, with higher scores indicating higher levels of endorsement for treatment acceptability.

Participants are asked to respond to questions used in previous research that assess the time spent in the past 24 hours (in minutes) in moderate-intensity physical activity and vigorous-intensity physical activity, in addition to time spent (in hours) on sedentary time. Response options were modified to allow participant to enter minutes rather than selecting a category. The three questions assessing sedentary time asked about how many hours were spent watching television, using the computer, and sitting. The investigators included an additional question assessing light-intensity physical activity.

The MPFI-24 was adapted for ecological momentary assessment (EMA) purposes, making it a self-report scale that assesses momentary psychological flexibility and inflexibility. Participants are asked to consider their day yesterday and rate their responses on a scale ranging from "NEVER True" to "ALWAYS True". Scores range from a minimum of 1.0 to 6.0, with higher scores reflecting higher levels of the domain being assessed (i.e., momentary psychological flexibility or inflexibility, etc.).

The "Contact With Values" subscale of the MPFI-4 adapted for EMA falls under the psychological flexibility factor and measures momentary connectedness to one's values. Participants will be asked to consider their experience the day before when rating their responses, and a sample item is: "I stuck to my deeper priorities in life."

The "Lack of Contact With Values" subscale of the MPFI-4 adapted for EMA falls under the psychological inflexibility factor and measures the extent to which one is not connected to their values at the moment. Participants will be asked to consider their experience the day before when rating their responses, and a sample item is: "My priorities and values often fell by the wayside."

Participants will be asked to rate the extent to which they feel 8 emotions in the present moment. The question is: "Rate how ___ you feel right now". The items are: "Content", "Relaxed", "Enthusiastic", "Joyful", "Anxious", "Angry", "Sad", and "Ashamed". The rating scale provided ranges from 1 (very slightly or not at all) to 5 (very much). As in past studies the investigators have conducted, the scale was adapted to replace "sluggish" with "ashamed."

Participants will be asked about their current motivation level to exercise. The question is: "How motivated are you right now to exercise?" The rating scale provided ranges from 1 (not at all) to 7 (extremely). This question will be asked both before and after the writing exercise.

Participants will be asked to rate how stressful their day was the day before. The question is: "How stressful was your day yesterday?" The rating scale provided ranges from 1 (not at all) to 7 (extremely).