Table 1.

The StepSmart Challenge key intervention components and potential mechanisms

Component	Activity/task	Potential mechanisms
Competition	The participating classes from the three intervention schools joined a pedometer competition using Fitbit Zip pedometers. Phase 1 (8 weeks) Inter-school pedometer competition Fitbit Zip pedometer data collected across all three intervention schools was collated to produce an aggregate school score. Teachers informed the participants on the progress of their school on a weekly basis. This information was also available to participants via The StepSmart Challenge website. Within schools team competition The team competition ran alongside the main school competition and involved approximately 10 teams within each school (five adolescents within each team). The highest placed team within each school at the end of phase 1 were the winners. Within schools individual competition Each week, all participants within each school competed to be the ‘walker of the week’ (the participant that had accumulated the most steps in the week) or the ‘most improved’ participant (the participant that had increased their step count the most from the previous week). Phase 2 Within schools individual competition Phase 2 began immediately after phase 1 ended. The inter-school and team competitions were replaced with an individual level competition within each school using the Fitbit Zip pedometers. The individual pedometer competition awarded the three participants in each school who had accumulated the most steps during this phase. Participants were encouraged to complete weekly challenges to increase their steps via The StepSmart Challenge website in this phase (e.g. ‘your weekly mission (should you choose to accept it) will be to walk or run the length of your street at least once every day’). Other missions encouraged participants to go walking with friends and family. This encouraged pro-social behaviour among participants in relation to physical activity outside of a school and team-based competition format.	The use of competition and challenges has been suggested as a way of making a physical activity intervention more engaging and enjoyable, which in turn can help maintain continued participation ([13] [64];).
Team working and social networks (e.g. working in teams for the intra-school competition and inter-school competition)	Selection of teams took current physical activity levels and friendship networks (using the social network data collected at baseline) into account, to ensure that each team (4–5 participants) included participants with a range of physical activity levels and at least one nominated friend.	The effect of peers on influencing physical activity in adolescents has been established ([17] [51];). Behavioural economics suggests this can be harnessed to counteract low levels of self-control [60]. Teams can also provide an opportunity for peer recognition which may increase feelings of self-competence, enjoyment and likelihood of maintained participation ([6] [34];).
Workbooks	A short workbook was given to participants at the start of the intervention. This included ‘fun-facts’, tips and challenges to promote physical activity behaviour individually and as part of a team. There was also as a section for the participant to record weekly step target (individual and team).	Self-determination theory proposes that a sense of relatedness with (the belonging to a group) is a fundamental psychological need for motivation [46]. This can also further foster a sense of connectedness to the team and thus team members could help encourage each other to increase physical activity levels.
Behavioural incentives	Phase 1 (8 weeks) Inter-school pedometer competition £1000 prize was awarded to the school with the highest aggregated number of steps at the end of the phase. Within schools team competition The team competition was comprised of social incentives such as the publication of results on The StepSmart Challenge website, and a trophy which was awarded to the leading team in each school at the end of the competition. Within schools individual competition The weekly ‘walker of the week’ and ‘most improved’ received a certificate, and a prize which varied over the course of the competition (e.g. selfie sticks, cinema tickets, gift certificates). Phase 2 (14 weeks) Within schools individual competition Phase 2 represented a tapered withdrawal from the extrinsically motivated behaviour change techniques towards more intrinsically motivated behaviours. Instead of weekly prizes, the three highest performing participants in each school were each presented with a trophy and a ‘goody bag’ comprising of an assortment of material incentives, e.g. selfie sticks, £10 vouchers. Other incentives were more abstract and took the form of ‘virtual badges’ to represent their achievements; this could be viewed on a participant’s personal profile on The StepSmart Challenge website.	Behavioural incentives contingent on successful performance of a behaviour provide positive reinforcement that can increase the frequency of the behaviour [54]. Behavioural incentives may also work to initiate physical activity in participants with low motivation due to present orientation and high levels of impulsivity [44].
Fitbit Zip pedometers	Participants were given a Fitbit Zip pedometer and asked to wear it every day of the intervention (phase 1 and phase 2). Fitbit Zips provided participants feedback on daily steps, and step data were uploaded to the study website via the Fitbit mobile application or a wireless dongle located at designated areas within schools.	Previous research using pedometers have shown success in increasing children and adolescents physical activity [32]. Pedometers provide real-time feedback. This continual feedback allows individuals to self-regulate behaviour by self-monitoring physical activity [45]. Regular feedback can provide positive feedback and instil feelings of competence when meaningful achievements are reached e.g. self-directed goals [46]. Regular feedback and opportunities to self-monitor behaviour can also counteract low motivation by keeping the activity salient [34].
The StepSmart Challenge website	Fitbit Zip data were uploaded to The StepSmart Challenge website and participants could review their daily/weekly scores and view the competition leader board. The website included the provision of motivational messages, weekly challenges and links to other physical activity resources.	The website provides regular feedback that shows participants their own physical activity in relation to the physical activity achieved by peers. This feedback might help keep the activity salient and motivate participants to increase their physical activity to normative levels (relative to the group) [64].
Facebook group	The Facebook group was created to provide support during the summer months (phase 2). This was a closed group, which was accessible to only The StepSmart Challenge participants from all three intervention schools. As a further protective measure teaching staff could view and moderate all communication via Facebook. This group provided participants with a convenient way to contact research staff, an opportunity to share their progress, and a platform for research staff to suggest different types of physical activity and provide motivational messages.	Facebook is a popular social network site among adolescents. Utilising this platform provides an opportunity for researchers to support and engage with participants, and participants to engage with each other during the summer months. This group was also used so researchers could post different opportunities to increase physical activity in the local area, and for participants to share their physical activity achievements.