Testing Self-Control as a Behavior Change Mechanism to Increase Physical Activity

Average daily steps baseline week, average daily steps between pretest and posttest, and average daily steps between posttest and followup. A higher score means more steps.

Time frame: Average daily steps baseline week (week 1); average daily steps between pretest and posttest (week 2-8); average daily steps between posttest and followup (week 9-12)

Population: Please note that some participants did not answer all questions/questionnaires because they were allowed to skip questions hence the discrepancy between measures. Some participants did not provide their step data.

The Brief Self-Control Scale was used to measure self-control. Items are assessed from 1 (not at all) to 5 (very much). A mean across all items will be calculated. A higher score means a higher score in self-control.

Time frame: Baseline (Pretest) T1, Week 8 (Posttest) T2, Week 12 (Follow-up) T3

Population: Please note that some participants did not answer all questions/questionnaires because they were allowed to skip questions hence the discrepancy between measures.

International Physical Activity Questionnaire - short version. A continuous score will be calculated expressed as MET (Metabolic Equivalents) minutes per week: Total MET-min/week = (Walk METs\*min\*days) + (Mod METs\*min\*days) + Vig METs\*min\*days). A higher score means higher level of physical activity.

Time frame: Baseline (Pretest) T1, Week 8 (Posttest) T2, Week 12 (Follow-up) T3

Population: Please note that some participants did not answer all questions/questionnaires because they were allowed to skip questions hence the discrepancy between measures.

The Brief Self-Control Scale was used to measure weekly self-control. Items are assessed from 1 (not at all) to 5 (very much). A mean across all items will be calculated. A higher score means a higher score in self-control. Participants were asked to answer the items with respect to the last week.

Time frame: Week 1, Week 2, Week 3, Week 4, Week 5, Week 6, Week 7

Population: Please note that some participants did not answer all questions/questionnaires because they were allowed to skip questions hence the discrepancy between measures.

To measure working memory capacity, we used the backward digit span test from the WAIS-III. The task includes increasingly longer series of digits, ranging from two to eight digits. Participants attempt to repeat them in the reverse order from which they were shown. The score is the longest string that is repeated exactly in reverse order. Digits are presented at a rate of one per second, beginning with a set size of two digits and progressing to eight digits. The accuracy score is the largest set size that was correctly reproduced. Possible range: 0 - 8. A higher score means a better outcome.

Time frame: Baseline (Pretest) T1, Week 8 (Posttest) T2, Week 12 (Follow-up) T3

Population: Please note that some participants did not answer all questions/questionnaires because they were allowed to skip questions hence the discrepancy between measures.

The Big Five Inventory 2 was used to assess the Big Five personality traits. Items are assessed from 1 (disagree strongly) to 5 (agree strongly). A mean across all items per personality trait will be calculated. A higher score means a higher score on a personality trait.

Time frame: Baseline (Pretest) T1, Week 8 (Posttest) T2, Week 12 (Follow-up) T3

Population: Please note that some participants did not answer all questions/questionnaires because they were allowed to skip questions hence the discrepancy between measures.

Nine items were used to assess how sure participants are that they will exercise under certain circumstances (e.g., when you are feeling under pressure or when you are away from home). Items were assessed from 1 (very sure) to 4 (not at all sure). A mean across all items will be calculated. A higher score means lower exercise self-efficacy.

Time frame: Baseline (Pretest) T1, Week 8 (Posttest) T2, Week 12 (Follow-up) T3

Population: Please note that some participants did not answer all questions/questionnaires because they were allowed to skip questions hence the discrepancy between measures.

Immediate episodic memory for verbal materials are tested using free recall of a word list drawn from the Rey Auditory-Verbal Learning Test. Participants are instructed to read carefully a list of 15 words which are presented at a rate of one second per word, and then to recall as many words as possible. In scoring the accuracy measure, one point is given for each correct response. Possible range: 0 - 15. A higher score means a better outcome.

Time frame: Baseline (Pretest) T1, Week 8 (Posttest) T2, Week 12 (Follow-up) T3

Population: Please note that some participants did not answer all questions/questionnaires because they were allowed to skip questions hence the discrepancy between measures.

The Satisfaction with life scale was used to assess satisfaction with life. Items were assessed from 1 (disagree strongly) to 7 (agree strongly). A mean across all items will be calculated. A higher score means a higher satisfaction with life.

Time frame: Baseline (Pretest) T1, Week 8 (Posttest) T2, Week 12 (Follow-up) T3

Population: Please note that some participants did not answer all questions/questionnaires because they were allowed to skip questions hence the discrepancy between measures.

12 items were used to assess sense of control. The scale consisted of two subscales: personal mastery (e.g., I can do just about anything I really set my mind to) and perceived constraints (e.g., What happens in my life is often beyond my control). All items were rated on a scale ranging from strongly agree (1) to strongly disagree (7). All items were coded so that a higher score reflected greater personal mastery and greater perceived constraints, respectively.

Time frame: Baseline (Pretest) T1, Week 8 (Posttest) T2, Week 12 (Follow-up) T3

Population: Please note that some participants did not answer all questions/questionnaires because they were allowed to skip questions hence the discrepancy between measures.

To measure attention switching and inhibitory control, we used the newly developed online app version of the Stop & Go Switch Task (SGST). The SGST requires alternating between the normal condition (i.e., respond Go to the stimulus Green and Stop to the stimulus Red) and the reverse condition (i.e., respond Stop to the stimulus Green and Go to the stimulus Red). For the SGST, the total number of correct responses across the mixed trials were calculated. Total range: 0 - 32. A higher score means a better outcome.

Time frame: Baseline (Pretest) T1, Week 8 (Posttest) T2, Week 12 (Follow-up) T3

Population: Please note that some participants did not answer all questions/questionnaires because they were allowed to skip questions hence the discrepancy between measures.