Effects of Wearable Fitness Trackers and Activity Adequacy Mindsets on Affect, Behavior, and Health: Longitudinal Randomized Controlled Trial

Background There is some initial evidence suggesting that mindsets about the adequacy and health consequences of one’s physical activity (activity adequacy mindsets [AAMs]) can shape physical activity behavior, health, and well-being. However, it is unknown how to leverage these mindsets using wearable technology and other interventions. Objective This research examined how wearable fitness trackers and meta-mindset interventions influence AAMs, affect, behavior, and health. Methods A total of 162 community-dwelling adults were recruited via flyers and web-based platforms (ie, Craigslist and Nextdoor; final sample size after attrition or exclusion of 45 participants). Participants received an Apple Watch (Apple Inc) to wear for 5 weeks, which was equipped with an app that recorded step count and could display a (potentially manipulated) step count on the watch face. After a baseline week of receiving no feedback about step count, participants were randomly assigned to 1 of 4 experimental groups: they received either accurate step count (reference group; 41/162, 25.3%), 40% deflated step count (40/162, 24.7%), 40% inflated step count (40/162, 24.7%), or accurate step count+a web-based meta-mindset intervention teaching participants the value of adopting more positive AAMs (41/162, 25.3%). Participants were blinded to the condition. Outcome measures were taken in the laboratory by an experimenter at the beginning and end of participation and via web-based surveys in between. Longitudinal analysis examined changes within the accurate step count condition from baseline to treatment and compared them with changes in the deflated step count, inflated step count, and meta-mindset conditions. Results Participants receiving accurate step counts perceived their activity as more adequate and healthier, adopted a healthier diet, and experienced improved mental health (Patient-Reported Outcomes Measurement Information System [PROMIS]-29) and aerobic capacity but also reduced functional health (PROMIS-29; compared with their no-step-count baseline). Participants exposed to deflated step counts perceived their activity as more inadequate; ate more unhealthily; and experienced more negative affect, reduced self-esteem and mental health, and increased blood pressure and heart rate (compared with participants receiving accurate step counts). Inflated step counts did not change AAM or most other outcomes (compared with accurate step counts). Participants receiving the meta-mindset intervention experienced improved AAM, affect, functional health, and self-reported physical activity (compared with participants receiving accurate step counts only). Actual step count did not change in either condition. Conclusions AAMs––induced by trackers or adopted deliberately––can influence affect, behavior, and health independently of actual physical activity. Trial Registration ClinicalTrials.gov NCT03939572; https://www.clinicaltrials.gov/ct2/show/NCT03939572

The CONSORT-EHEALTH checklist is intended for authors of randomized trials evaluating web-based and Internet-based applications/interventions, including mobile interventions, electronic games (incl multiplayer games), social media, certain telehealth applications, and other interactive and/or networked electronic applications. Some of the items (e.g. all subitems under item 5 -description of the intervention) may also be applicable for other study designs.
The goal of the CONSORT EHEALTH checklist and guideline is to be a) a guide for reporting for authors of RCTs, b) to form a basis for appraisal of an ehealth trial (in terms of validity) CONSORT-EHEALTH items/subitems are MANDATORY reporting items for studies published in the Journal of Medical Internet Research and other journals / scientific societies endorsing the checklist.
As the CONSORT-EHEALTH checklist is still considered in a formative stage, we would ask that you also RATE ON A SCALE OF 1-5 how important/useful you feel each item is FOR THE PURPOSE OF THE CHECKLIST and reporting guideline (optional).
Mandatory reporting items are marked with a red *. In the textboxes, either copy & paste the relevant sections from your manuscript into this form -please include any quotes from your manuscript in QUOTATION MARKS, or answer directly by providing additional information not in the manuscript, or elaborating on why the item was not relevant for this study. yes: all primary outcomes were significantly better in intervention group vs control partly: SOME primary outcomes were significantly better in intervention group vs control no statistically significant difference between control and intervention potentially harmful: control was significantly better than intervention in one or more outcomes inconclusive: more research is needed Other: not submitted yet -in early draft status not submitted yet -in late draft status, just before submission submitted to a journal but not reviewed yet submitted to a journal and after receiving initial reviewer comments submitted to a journal and accepted, but not published yet If this is a JMIR submission, please provide the manuscript tracking number under "other" (The ms tracking number can be found in the submission acknowledgement email, or when you login as author in JMIR. If the paper is already published in JMIR, then the ms tracking number is the four-digit number at the end of the DOI, to be found at the bottom of each published article in JMIR) T   1  a  )  T  I  T  L  E  :  I  d  e  n  t  i  f  i  c  a  t  i  o  n  a  s  a  r  a  n  d  o  m  i  z  e  d  t  r  i  a  l  i  n  t  h  e  t  i  t  l  Identify the mode of delivery. Preferably use "web-based" and/or "mobile" and/or "electronic game" in the title. Avoid ambiguous terms like "online", "virtual", "interactive". Use "Internet-based" only if Intervention includes non-web-based Internet components (e.g. email), use "computer-based" or "electronic" only if offline products are used. Use "virtual" only in the context of "virtual reality" (3-D worlds). Use "online" only in the context of "online support groups". Complement or substitute product names with broader terms for the class of products (such as "mobile" or "smart phone" instead of "iphone"), especially if the application runs on different platforms. Copy and paste relevant sections from manuscript title (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study Copy and paste relevant sections from the manuscript abstract (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "Participants received an Apple Watch to wear for 5 weeks, which was equipped with an app that recorded step count and could display a (potentially manipulated) step count on the watch face. After a baseline week of receiving no feedback about step count, participants were randomly assigned to one of four experimental groups: they received either (1) accurate step count (reference group, n = 41), 40% deflated step count (n = 40), 40% inflated step count (n = 40), or accurate step count + a web-based meta-mindset intervention teaching participants the value of adopting more positive AAMs (n = 41)." Clarify the level of human involvement in the abstract, e.g., use phrases like "fully automated" vs. "therapist/nurse/care provider/physician-assisted" (mention number and expertise of providers involved, if any). Copy and paste relevant sections from the manuscript abstract (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study The methods section of the abstract makes it clear that interventions were delivered via the Apple Watch app and through a web-based intervention. We thus did not consider it necessary to clarify that there was no human involvement.  t  o  -f  a  c  e  a  s  s  e  s  s  m  e  n  t  s  i  n  t  h  e  M  E  T  H  O  D  S  s  e  c  t  i  o  n  o  f  t  h  e  A  B  S  T  R  A  C  T Mention how participants were recruited (online vs. offline), e.g., from an open access website or from a clinic or a closed online user group (closed usergroup trial), and clarify if this was a purely web-based trial, or there were face-to-face components (as part of the intervention or for assessment). Clearly say if outcomes were self-assessed through questionnaires (as common in web-based trials Copy and paste relevant sections from the manuscript abstract (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "162 community-dwelling adults were recruited via flyers and online platforms (i.e., Craigslist, Nextdoor; final sample size after attrition/ exclusion of 45 participants). Participants received an Apple Watch to wear for 5 weeks, which was equipped with an app that recorded step count and could display a (potentially manipulated) step count on the watch face. After a baseline week of receiving no feedback about step count, participants were randomly assigned to one of four experimental groups: they received either (1) accurate step count (reference group, n = 41), 40% deflated step count (n = 40), 40% inflated step count (n = 40), or accurate step count + a web-based meta-mindset intervention teaching participants the value of adopting more positive AAMs (n = 41). Participants were blinded to condition. Outcome measures were taken in lab by an experimenter in the beginning and end of participation, and via web-based surveys in between." Copy and paste relevant sections from the manuscript abstract (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "162 community-dwelling adults were recruited via flyers and online platforms (i.e., Craigslist, Nextdoor; final sample size after attrition/ exclusion of 45 participants)." "After a baseline week of receiving no feedback about step count, participants were randomly assigned to one of four experimental groups: they received either (1) accurate step count (reference group, n = 41), 40% deflated step count (n = 40), 40% inflated step count (n = 40), or accurate step count + a web-based meta-mindset intervention teaching participants the value of adopting more positive AAMs (n = 41)." Conclusions/Discussions in abstract for negative trials: Discuss the primary outcome -if the trial is negative (primary outcome not changed), and the intervention was not used, discuss whether negative results are attributable to lack of uptake and discuss reasons. Copy and paste relevant sections from the manuscript abstract (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "Participants receiving accurate step count perceived their activity as more adequate and healthier, adopted a healthier diet, and experienced improved mental health (PROMIS-29) and aerobic capacity, but also reduced functional health (PROMIS-29) (compared to their nostep-count baseline). Participants exposed to deflated steps perceived their activity as more inadequate, ate more unhealthily and experienced more negative affect, reduced selfesteem and mental health, and increased blood pressure and heart rate (compared to participants receiving accurate steps). Inflated steps did not change AAM and most other outcomes (compared to accurate steps). Participants receiving the meta-mindset intervention experienced improved AAM, affect, functional health, and self-reported physical activity (compared to participants receiving accurate steps only). Actual step count did not change in either condition." Some possible explanations for negative outcomes are discussed in the paper, but as those are speculative, we are not including them in the abstract. In the context of physical activity, initial research suggests that people hold mindsets about their physical activity level's adequacy and its corresponding health consequences (activity adequacy mindsets, AAMs) [21]. These mindsets are based partly on individuals' actual physical activity. However, they are often not a mere reflection of one's objective activity levels. For example, even among individuals who get the same objective amount of physical activity, some may believe that their activity level is adequate and benefits their health (i.e., adequate activity mindset). In contrast, others may believe that their activity is inadequate and harms their health (i.e., inadequate activity mindset). Individuals' AAMs may significantly affect their health, wellbeing, and even longevity, regardless of their actual physical activity. In epidemiological research, data from three nationally representative samples showed that people who perceived themselves as less active than other people their age (a proxy for the inadequate activity mindset) had an up to 72% higher mortality risk 21 years later than those who perceived themselves as more active, controlling for actual amounts of activity (assessed through comprehensive selfreport questionnaires and objective accelerometer data) [22]. Similarly, perceived physical activity relative to others predicts cognitive function in older adults [23]. The opposite, perceived sedentary behavior relative to others, is associated with psychological stress [24].
In experimental research, one study examined a sample of hotel room attendants, who objectively met physical activity guidelines through their work, but still perceived themselves as inactive because they were unaware that their work counted as exercise. An intervention informing room attendants that their work constituted adequate exercise resulted in reduced weight, body fat, and blood pressure one month later, compared to a control group [25]. Another study [21] investigated the effects of viewing the official U.S. physical activity guidelines (prescribing a relatively high amount of activity) compared to guidelines that prescribed a lower amount of activity on AAM. Individuals exposed to guidelines prescribing a lower amount of physical activity adopted more adequate activity mindsets, which in turn predicted greater self-efficacy, engagement in physical activity, and perceived health 1 week later. Moreover, a meta-analysis comparing the effects of exercise training and placebo-exercise training (i.e., types of exercise without a known pharmacological biochemical or physical mechanism of action) showed that the mere https://docs.google.com/forms/d/e/1FAIpQLSfZBSUp1bwOc_OimqcS64RdfIAFvmrTSkZQL2-3O8O9hrL5Sw/viewform?hl=en_US&formkey=dGlKd2Z2Q1lNS… 17/58 pharmacological, biochemical, or physical mechanism of action) showed that the mere belief that one is engaging in exercise accounted for half of the psychological benefits of exercise (e.g., reduced anxiety and depression) [26]. Presumably, these effects occurred because participants had adequate activity mindsets and thus expected wellbeing benefits. Though these studies provide suggestive evidence that AAMs may affect health and wellbeing, others have yielded less promising results. In particular, one intervention failed to induce positive changes in mindsets about physical activity [27], and another was unable to produce effects on health outcomes in healthy adolescents [28]. Moreover, research and public attention on the important effects of actual physical activity behavior on health has continued to predominate [1], at the expense of the insight that mindsets may also matter." "The basic idea behind wearable activity trackers is simple: help users get adequate physical activity by providing feedback about their progress towards specific activity goals (e.g., 10,000 steps a day, standing for at least 1 minute during 12 hours of the day, or exercising for a target number of minutes). Much research attention has been devoted to eHealth and mHealth interventions to promote physical activity [43], and commercial high-end wearables now also incorporate other behavior change techniques (BCTs) such as highlighting the discrepancy between current behavior and goal, biofeedback, social comparison and social support [13]. Unfortunately, the evidence about activity trackers' effectiveness is inconclusive. Some meta-analyses find improvements in physical activity [9] and body weight [44], but others show no or even pernicious effects when comparing wearable-based interventions to alternative interventions (rather than inactive controls) [10,11,45]." "AAMs have the potential to improve health and wellbeing, but to date, interventions to leverage AAMs at scale are lacking. First, to establish causal effects, research has used deceptive methods to manipulate mindsets [21], which would be unethical outside of the research context. Second, a high level of specificity makes interventions challenging to scale. For example, the intervention informing room attendants that their work satisfies exercise guidelines [25] cannot be adapted to less physically demanding jobs and neglects other aspects of a person's lifestyle (e.g., carrying children). Third, interventions teaching participants explicitly to adopt a mindset (rather than inducing it stealthily) have shared information about the content of the desirable mindset (e.g., "my work is good exercise"), but not about mindsets per se (e.g., "assuming that my physical activity is inadequate is a mindset that is not necessarily true") or their effects (e.g., "my mindsets can influence my health and performance"). Interventions lacking such meta-cognitive knowledge about mindsets may be less likely to stick in the long run when individuals' lifestyles change, or environments present inconsistent information." "There is initial evidence for the effectiveness of meta-mindset interventions. In one study, employees were taught that stress can have both debilitating and enhancing effects and that stress mindsets can influence the effects of stress in a self-fulfilling manner. This intervention enabled participants to adopt a stress-is-enhancing mindset and improved their physical health, health satisfaction, and work performance [46]. Another intervention successfully encouraged students to deliberately adopt a growth mindset about https://docs.google.com/forms/d/e/1FAIpQLSfZBSUp1bwOc_OimqcS64RdfIAFvmrTSkZQL2-3O8O9hrL5Sw/viewform?hl=en_US&formkey=dGlKd2Z2Q1lNS… 18/58 ? * Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "This research explores four questions arising from the theory and evidence reviewed above. First, we examine if receiving step count feedback from a wearable tracker (here, Apple Watch) affects activity adequacy mindset (AAM). Second, we experimentally manipulate step count feedback with the intent of inducing different levels of AAM and thereby investigate whether AAMs causally influence health and wellbeing (e.g., weight and blood pressure; anxiety and depression; ability to engage in everyday tasks) independently of how active individuals actually are. Third, we explore AAMs' effects on several affective and behavioral determinants of health (e.g., positive and negative affective experiences; physical activity and diet). Fourth, we test the effectiveness of a meta-mindset intervention designed to empower individuals to deliberately adopt AAMs that can benefit their health and wellbeing." Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "Design and manipulations. This study used a parallel trial design (allocation ratio 1:1:1:1).
Participants were assigned to one of four conditions--(1) accurate step count (n = 41), (2) deflated step count (n = 40), (3) inflated step count (n = 40), or (4) meta-mindset intervention plus accurate step count (n = 41)--via criteria-based randomization (CBR) [49,50]. Week 1 was a baseline week, during which no step count feedback or interventions were delivered. The meta-mindset intervention was delivered on day 7, and the Apple Watch step count was displayed to all participants starting on day 8." Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study not applicable, as there were not important changes to methods after trial Bug fixes, Downtimes, Content Changes: ehealth systems are often dynamic systems. A description of changes to methods therefore also includes important changes made on the intervention or comparator during the trial (e.g., major bug fixes or changes in the functionality or content) (5-iii) and other "unexpected events" that may have influenced study design such as staff  Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study There were no significant bugs to report Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "To be eligible to participate, they had to meet the following criteria assessed via a webbased prescreen survey: walking as the primary source of physical activity in the prior six months (to ensure relevance of the step count manipulation); health status allows engagement in physical activity according to the Physical Activity Readiness Questionnaire [49]; not pregnant (as natural changes in weight and body composition during pregnancy would invalidate results); possession of an iPhone 5 S or newer (to allow connecting an Apple Watch); and limited exposure to activity tracking technology or apps (to ensure participants were naïve to their daily step count)." Computer / Internet literacy is often an implicit "de facto" eligibility criterion -this should be explicitly clarified. Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study Computer/ internet literacy was an implicit eligibility criterion as participants had to complete "a web-based prescreen survey" and possess "an iPhone 5 S or newer (to allow connecting an Apple Watch)" a c e a s s e s s m e n t s : Open vs. closed, web-based vs. face-to-face assessments: Mention how participants were recruited (online vs. offline), e.g., from an open access website or from a clinic, and clarify if this was a purely webbased trial, or there were face-to-face components (as part of the intervention or for assessment), i.e., to what degree got the study team to know the participant. In online-only trials, clarify if participants were quasi-anonymous and whether having multiple identities was possible or whether technical or logistical measures (e.g., cookies, email confirmation, phone calls) were used to detect/prevent these. Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "Participants were a diverse sample of 162 West-Coast community-dwelling adults, recruited via flyers and online platforms (i.e., Craigslist, Nextdoor). To be eligible to participate, they had to meet the following criteria assessed via a web-based prescreen survey" "Each participant attended a personal onboarding and offboarding session at the start and end of their 5-week study participation (Fig. 1). Experimenters were blind to participants' experimental condition." "Throughout the following 5 weeks, participants' step count was tracked by the Apple Watch. Additionally, participants completed weekly web-based surveys assessing affective and behavioral processes and daily check-ins to ensure step count awareness. One researcher monitored participants' survey response rates and watch activity to ensure study adherence. When step counts had not been updated to the cloud database for an extended time, researchers communicated with participants via text message or email to remind them to wear the watch or assist with any technical issues. At the end of the 5 weeks, participants returned for the offboarding session, completing the same measures as in the onboarding session." Information given during recruitment. Specify how participants were briefed for recruitment and in the informed consent procedures (e.g., publish the informed consent documentation as appendix, see also item X26), as this information may have an effect on user self-selection, user expectation and may also bias results. Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "The posting advertised an opportunity to participate in a paid research study to develop more effective fitness trackers." "Participants were briefed with the cover story that the study aimed to develop more accurate fitness tracking algorithms. They then provided informed consent (footnote: Full consent procedures and form available in supplemental materials.) and received a handout explaining the benefits of walking for health and wellbeing, anchoring them on the idea that every additional step is valuable, even at low physical activity levels. Participants were also instructed to use only the AccuSteps app for physical activity information and to wear the Apple watch every day (except when sleeping, showering, or swimming). They then completed psychological and physiological assessments." "At the end of the 5 weeks, participants returned for the offboarding session, completing the same measures as in the onboarding session. Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "Each participant attended a personal onboarding and offboarding session in a laboratory of the Computer Science department at the start and end of their 5-week study participation (Fig. 1). [...] They then completed web-based psychological assessments and the experimenter took physiological assessments. Throughout the following 5 weeks, participants' step count was tracked by the Apple Watch. Additionally, participants completed weekly web-based surveys assessing affective and behavioral processes and daily check-ins to ensure step count awareness. [...] At the end of the 5 weeks, participants returned for the offboarding session, completing the same measures as in the onboarding session. "  Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study Your answer Revisions and updating. Clearly mention the date and/or version number of the application/intervention (and comparator, if applicable) evaluated, or describe whether the intervention underwent major changes during the evaluation process, or whether the development and/or content was "frozen" during the trial.
Describe dynamic components such as news feeds or changing content which may have an impact on the replicability of the intervention (for unexpected events see item 3b Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "Trial registration: ClinicalTrials.gov Identifier NCT03939572. Data and code will be made available at osf.io/8ea5r/?view_only=35003df8eb984ae888547a9eab27eb21." "Complete models, results, and raw data are reported in the supplemental materials." Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study Participants did not have to pay for any accesses. They were provided access to the app and web-based surveys by the experimenters. They were paid for study participation. "In the onboarding session, participants received an Apple Watch Series 1 equipped with "AccuSteps", a step-tracking app developed by the research team that can collect and manipulate a user's step count and ambiently displays that information as a widget on the watch face." "They were then fully debriefed, thanked, and paid $175 for satisfactory participation." Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "This research explores four questions arising from the theory and evidence reviewed above. First, we examine if receiving step count feedback from a wearable tracker (here, Apple Watch) affects activity adequacy mindset (AAM). Second, we experimentally manipulate step count feedback with the intent of inducing different levels of AAM and thereby investigate whether AAMs causally influence health and wellbeing (e.g., weight and blood pressure; anxiety and depression; ability to engage in everyday tasks) independently of how active individuals actually are. Third, we explore AAMs' effects on several affective and behavioral determinants of health (e.g., positive and negative affective experiences; physical activity and diet). Fourth, we test the effectiveness of a meta-mindset intervention designed to empower individuals to deliberately adopt AAMs that can benefit their health and wellbeing." "participants received an Apple Watch Series 1 equipped with "AccuSteps", a step-tracking app developed by the research team that can collect and manipulate a user's step count and ambiently displays that information as a widget on the watch face." "Design and manipulations. This study used a parallel trial design (allocation ratio 1:1:1:1).
Participants were assigned to one of four conditions--(1) accurate step count (n = 41), (2) deflated step count (n = 40), (3) inflated step count (n = 40), or (4) meta-mindset intervention plus accurate step count (n = 41)--via criteria-based randomization (CBR) [49,50]. Week 1 was a baseline week, during which no step count feedback or interventions were delivered. The meta-mindset intervention was delivered on day 7, and the Apple Watch step count was displayed to all participants starting on day 8.
Step Count Feedback Manipulations. After the no-feedback baseline week, participants in the accurate step count condition started to view their step count as recorded by the Apple Watch (Fig. 2). This condition allowed us to examine whether simply wearing an activity tracker and receiving step count feedback (vs. no feedback) was associated with changes in AAM and other outcomes. After the baseline week, participants in the deflated and inflated step count conditions started to view their step count, as recorded by the Apple Watch but automatically deflated or inflated by 40% (respectively) by our AccuSteps app. All participants believed that they were receiving their accurate step count (confirmed by poststudy interviews). Meta-Mindset Intervention. The meta-mindset intervention was included in the first weekly survey and consisted of three videos and reflection activities. The 3-5-minute-long videos informed participants about health-related mindsets in general, AAMs in particular, and how mindsets can create self-fulfilling effects. The reflection activity prompted participants to notice any activities they had done in the last week that took some physical effort (e.g., walking, housework, and other activities they might not usually think of as exercise). Next, they were asked to count all of these activities as beneficial exercise and celebrate themselves for this physical activity. The final component encouraged people to think about their activity's short-and long-term benefits (e.g., improved mood, sleep; lower blood pressure, protection from heart disease). Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "Participants were also instructed to use only the AccuSteps app for physical activity information and to wear the Apple watch every day (except when sleeping, showering, or swimming)."

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Clarify the level of human involvement (care providers or health professionals, also technical assistance) in the e-intervention or as co-intervention (detail number and expertise of professionals involved, if any, as well as "type of assistance offered, the timing and frequency of the support, how it is initiated, and the medium by which the assistance is delivered". It may be necessary to distinguish between the level of human involvement required for the trial, and the level of human involvement required for a routine application outside of a RCT setting (discuss under item 21 -generalizability). Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "Each participant attended a personal onboarding and offboarding session in a laboratory of the Computer Science department at the start and end of their 5-week study participation (Fig. 1). Experimenters were blind to participants' experimental condition. In the onboarding session, participants received an Apple Watch Series 1 equipped with "AccuSteps", a steptracking app developed by the research team that can collect and manipulate a user's step count and ambiently displays that information as a widget on the watch face. Participants were briefed with the cover story that the study aimed to develop more accurate fitness tracking algorithms. They then provided informed consent and received a handout explaining the benefits of walking for health and wellbeing, anchoring them on the idea that every additional step is valuable, even at low physical activity levels. Participants were also instructed to use only the AccuSteps app for physical activity information and to wear the Apple watch every day (except when sleeping, showering, or swimming). They then completed web-based psychological assessments and the experimenter took physiological assessments. Throughout the following 5 weeks, participants' step count was tracked by the Apple Watch. Additionally, participants completed weekly web-based surveys assessing affective and behavioral processes and daily check-ins to ensure step count awareness. One researcher monitored participants' survey response rates and watch activity to ensure study adherence. When step counts had not been updated to the cloud database for an extended time, researchers communicated with participants via text message or email to remind them to wear the watch or assist with any technical issues. At the end of the 5 weeks, participants returned for the offboarding session, completing the same measures as in the onboarding session. They were then fully debriefed, thanked, and paid $175 for satisfactory participation." Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "One researcher monitored participants' survey response rates and watch activity to ensure study adherence. When step counts had not been updated to the cloud database for an extended time, researchers communicated with participants via text message or email to remind them to wear the watch or assist with any technical issues." Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study Participants "received a handout explaining the benefits of walking for health and wellbeing, anchoring them on the idea that every additional step is valuable, even at low physical activity levels." "Additionally, participants completed weekly web-based surveys assessing affective and behavioral processes and daily web-based check-ins to ensure step count awareness." Copy and paste relevant sections from manuscript title (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study From supplemental materials: "Our target sample size was 160, but we overrecruited due to projected attrition. A total of 207 volunteers were randomized to one of four conditions (accurate, deflated, inflated and meta-mindset intervention Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "Participants were assigned to one of four conditions--(1) accurate step count (n = 41), (2) deflated step count (n = 40), (3) inflated step count (n = 40), or (4)  Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study From supplemental materials: "Random assignment was conducted in between onboarding and day 8 of study participation by an experimenter who did not interact with participants to ensure double blindness."

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Specify who was blinded, and who wasn't. Usually, in web-based trials it is not possible to blind the participants [1, 3] (this should be clearly acknowledged), but it may be possible to blind outcome assessors, those doing data analysis or those administering co-interventions (if any). Informed consent procedures (4a-ii) can create biases and certain expectations -discuss e.g., whether participants knew which intervention was the "intervention of interest" and which one was the "comparator". Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "Participants were also unaware that there were any experimental conditions." Imputation techniques to deal with attrition / missing values: Not all participants will use the intervention/comparator as intended and attrition is typically high in ehealth trials. Specify how participants who did not use the application or dropped out from the trial were treated in the statistical analysis (a complete case analysis is strongly discouraged, and simple imputation techniques such as LOCF may also be problematic [4]). Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study Your answer Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study Your answer Report multiple "denominators" and provide definitions: Report N's (and effect sizes) "across a range of study participation [and use] thresholds" [1], e.g., N exposed, N consented, N used more than x times, N used more than y weeks, N participants "used" the intervention/comparator at specific pre-defined time points of interest (in absolute and relative numbers per group). Always clearly define "use" of the intervention. In addition to primary/secondary (clinical) outcomes, the presentation of process outcomes such as metrics of use and intensity of use (dose, exposure) and their operational definitions is critical. This does not only refer to metrics of attrition (13-b) (often a binary variable), but also to more continuous exposure metrics such as "average session length". These must be accompanied by a technical description how a metric like a "session" is defined (e.g., timeout after idle time)