Table 4.

Themes, findings, and supporting quotations identified in the thematic synthesis.

Review Aim	Analytical Theme	Descriptive Theme	Subthemes	Number of Supporting Studies	Findings and Supporting Quotations
Feasibility	Perceived facilitators and barriers of using a wearable may impact device use	Factors impacting the use of wearables	Device technical difficulties	8	Some adolescents reported general barriers to technology, such as access to a computer [61] or the Internet [33], that may limit device use. Some participants reported difficulties with charging and syncing devices (n = 3): “They didn’t charge properly” (Kidfit [60]). Other participants reported daily syncing and charging as burdensome: “Sometimes I forgot, it’s like getting a little bit annoying to have to like do it every day” (Fitbit Flex [49]).
			Device design impacts wearability	10	Some wrist-worn devices were deemed uncomfortable and bulky: “The wristband wasn’t comfortable” (Kidfit [60]). “I kind of got annoyed with it at the end because of the bulkiness… It was a factor in like I didn’t really want to have to wear it” (MOVband [61]). However, participants were worried they would lose the Fitbit One due to its small size: “I didn’t like it because it was too tiny, I thought I was going to lose it” [33].
			Removal for sports and daily activities	7	Some participants disliked that the wearable was unable to capture their activity during sports: “Because I kind of like it when you can see that you’re getting really high [step counts] and not being able to wear it during sporting events. I wasn’t able to see what I was really getting and how high I could really get” (MOVband [61]). Participants reported forgetting to wear the device following removal due to daily activities, such as showering and getting changed: “Now that it’s not waterproof, I like forget to put it back on after a shower” (Polar Active [58]). “Changed into my pyjamas I was like, ‘Oh, I forgot I had that’” (Fitbit One [33]).
Acceptability	Affective attitude: Feelings towards using wearables	Participants’ feelings of enjoyment, boredom, frustration, and distrust towards using wearables.	Enjoyment of using wearables	8	Participants enjoyed using the devices, which may be attributed to their gamification components: “It was fun to compare steps” (Fitbit One [33]). “It felt like a computer game” (Samsung Galaxy Gear HR [65]) “It was fun. It’s almost like a game” (MOVband [61]).
			Novelty effect	6	Participants reported a potential novelty effect of using the device, which may be attributed to boredom: “It’s fun for a bit … the novelty rubs off and just... oh well, I don’t really care anymore” (Fitbit Flex [49]). “I used it for the first 4 weeks, then just gave up” (Fitbit Charge [57]). One parent reported their child was not interested in owning a device after the study: “I said, ‘oh would you want to wear them, like would you want one of your own?’ They said ‘no, we’ve kind of used it now’” (Kidfit [60]).
			Questions regarding the integrity of wearables	4	Some participants admitted to testing the integrity of the device by shaking the device or counting their steps: “I tried to count actually how many steps I do, and then I looked at the Fitbit, and it was like 16 off” (Fitbit One [33]). “I would like shake it to see if it’s working and sometimes it wouldn’t” (Fitbit Flex [49]). One adolescent suggested people could “cheat” their PA data, by shaking the device: “But sometimes people can cheat on that, I think” (Fitbit Flex [49]).
			Disappointment due to child restrictions and parental control	2	Child restrictions resulted in feelings of disappointment in younger participants: “My mom feels like she didn’t really want this [software] on my laptop” (MOVband [61]). “Bit disappointed that she couldn’t access her own information … because they’d want to see what they’d scored” (Kidfit [60]).
	Perceived effectiveness and intervention coherence: wearables perceived ease of use, interpretation of PA outputs and impact on PA	Wearables ease of use, understanding of PA outputs, and perceived impact on PA varies between devices and individuals.	Understanding how to use wearables and interpret PA outputs	6	Participants reported wearables were easy to use, and PA outputs were easy to understand: “It was kind of easy to understand. It wasn’t confusing at all” (Sqord [62]). However, some participants reported a lack of understanding of how to use device features: “I was trying to like add more onto goals and stuff I found it like hard to use and I just like stopped using it” (Fitbit Flex [49]). “I sometimes look at the challenges but I don’t really know what they are”, “It’s really, really confusing how to get sqoins and stuff” (Sqord [62]).
			A perceived increase in PA levels	8	Some adolescents suggested the mere presence of the device made them more active: “Just knowing it’s on your wrist, it makes me want to be more active” (Fitbit Flex [68]). Most participants referred to a change in lifestyle: “So, we knew [due to the feedback report] we needed to go out a bit more on a Sunday, which we do actually do quite a bit now” (Polar Active [58]). “I would like try to do extra, like offer to take the dog out instead of complaining about it” (Fitbit One [33]). However, one adolescent believed this increase in PA would diminish when they no longer had access to the device: “Cuz I won’t see the results that I done” (Samsung Galaxy Gear HR [65]).
			Wearables do not impact PA levels	3	Some participants reported the wearable did not impact their PA levels. However, these participants perceived themselves to be active, and used the device to confirm their beliefs about their active lifestyle: “We were already pretty active so I don’t know” (Fitbit Zip [71]). “I think it just showed me what I was doing” (MOVband [61]).
Mechanisms of action	Perceived mechanisms of action underlying wearables impact on PA	Wearables may motivate or discourage PA via BCTs: feedback, self-monitoring and goal setting, competition, and rewards and incentives.	Feedback, self-monitoring, and goal-setting	9	Participants used immediate feedback to increase their PA levels, and awareness of their PA levels: “When it says get off the couch, he did respond to that” (Kidfit [60]). “Yeah, it makes you so aware of how many or how active you are and then you wanna try to harder” (Fitbit Flex [49]). Participants disliked feedback displayed as a visual representation, or that was only displayed via the partnering app: “What was the flower about?” (Fitbit One [33]) “Didn’t like the fact, unlike this [Fitbit] where you can see your steps instantaneously” (Kidfit [60]). Feedback promoted the use of self-monitoring and goal setting to increase PA. Participants reported a conscious effort to increase their PA to reach their PA goal, or when achieved, increase their PA goal: “In two days, I did 15 miles. My goal was, the next day, to do 6 more miles”, “I want to reach my goal” (MOVband [61]). However, some adolescents reported that predetermined goals (10,000 steps/day) may create feelings of pressure and guilt: “You can feel under pressure to do a certain amount of steps or to be better than what you’re maybe capable of” (Fitbit Charge [57]).
			Competition with the self and others	6	Participants suggested that “beating” their previous score, or their friends’ score, encouraged them to be more physically active: “I wanted to beat my score”, “I always tried to push myself to the next lesson … to try and get a higher mark” (Samsung Galaxy Gear HR [65]). Parents suggested that children may enjoy collective school competitions: “It would be great to have a competition between the classes, rather than amongst each individual kid, because then they’re helping each other along” (Kidfit [60]). However, 3 studies reported that competition may create feelings of pressure and guilt: “Some people maybe feel peer pressure to do fitness, to keep their steps and stuff up”, “You can sometimes feel guilty … I couldn’t let someone else beat me” (Fitbit Charge [57]).
			Rewards and incentives	3	Participants reported enjoying rewards and incentives, including social rewards: “I really like that, um, you get rewards”, “I like how you can “like” things because then it makes me feel good when people like my stuff because it makes me feel happy” (Zamzee [62]). However, some participants suggested virtual rewards, such as badges, were not considered an incentive to be physically active: “It’s not like a huge achievement or anything” (Fitbit Flex [68]).