The data presented here indicate that friendship groups are key influences on the location and type of physical activity in which children engage. Friendship groups are not uniform and differ for individual children with many children belonging to several groups and engaging in different activities with the different groups. Participants reported that membership of several groups was desirable as it presented alternative opportunities for activity and prevented boredom. Diverse friendship groups may therefore be a mediator of higher levels of physical activity because if a child has more friendship resources to draw upon he or she may be more active. Moreover, if one friendship group dissolves the child can still be active with other groups, thereby providing a "safety net" against inactivity. Finding ways to help children to develop physical activity behaviors with several different groups could be a key method for families and policy makers to increase youth physical activity.
The potential utility of membership of several friendship groups raises a number of issues about current youth physical activity research. A large proportion of youth physical activity research is conducted within schools and is based on the underlying premise that the factors that affect physical activity will be based upon either key psychosocial constructs , parental or home factors [32, 33] or more recently the physical environment  in which the child resides. Studies do not focus on the extent to which friends from the neighborhood, children of parental friends or peers from organized sport or non-sport locations influence physical activity. It seems plausible that a greater understanding of the factors that influence youth physical activity participation will be achieved by identifying these groups and their mechanisms of influence on youth physical activity. To achieve this objective there is a need to develop new measures of assessing friendship group affiliation and specifically if membership of several friendship groups results in higher levels of physical activity.
The results presented here suggest that children are initiated into physical activity via co-participation, peer verbal encouragement or modeling by another child. Modeling and verbal persuasion are key processes in the development of self-efficacy  which has consistently been related to youth physical activity levels [36, 37]. Our data therefore suggest that many youth are organically increasing their own self-efficacy and thus we should explore how we can build on these processes to help youth become more active. Moreover, participants were members of several groups and thus it seems plausible that the initiation into friendship groups likely occurred by an existing friend initiating a child into a physical activity friendship group via one or more of the above strategies. Findings therefore suggest that simple strategies to build self-efficacy via co-participation, peer verbal encouragement or modeling could therefore be effective means of increasing physical activity and broadening a child's number of friendship groups. For example, encouraging children to "sign up a friend" to join them in attending an activity may spark the friend's interest in that form of physical activity. This could be achieved by providing children with "2 for the price of 1" vouchers for key physical activity venues. These strategies could easily be incorporated into physical activity interventions.
Consistent with previous research [38–40], participants reported that enjoyment of physical activity and spending time with friends were the key influences on maintaining participation in physical activity. Interestingly, our findings extend that work by indicating that physical activity is often seen as a more pleasurable way to spend time than screen-based sedentary behaviors. Therefore strategies or messages that directly contrast the perceived merits of physical activity and screen-viewing and reinforce the social aspects of physical activity could form components of strategies to maintain activity among youth. Moreover, interventions that directly focus on providing social opportunities for activity may be effective activity promotion mechanisms to harness the intrinsic enjoyment of physical activity that was expressed by these young people.
In this study we found that the association between physical activity ability and social status was complex and differed by gender. Among boys, physical activity ability was associated with a positive social status. Our findings are therefore consistent with previous work which has shown that physical activity competency is associated with both perceived and actual peer group acceptance and peer affiliation among youth . For girls, our data suggest that the link between physical prowess and friendship groups is less clear, with physical activity ability being perceived either positively or negatively and this perception appearing to be related to the friendship groups to which the girls belong and the attitudes of that group. As negative childhood physical activity experiences have been shown to adversely affect adult physical activity participation , it seems plausible that the friendship groups to which a child belongs is likely to be a moderator of this association. Therefore, further exploration of the link between social status, physical ability and group norms among youth is needed, particularly whether using this link between physical activity and group affiliation could be a means to engage low-active boys into physical activity. Hence, we need to understand more about how allegiance to friendship groups among girls is formed and its relationship to physical activity participation among girls.
Although the sample in this study is relatively large for qualitative work and we attempted to recruit participants from a range of schools, it is difficult to generalize to the larger population. It is also important to recognize that as the data were collected in schools only students attending schools on data collection were able to participate. As such, the data presented here may not represent the view of children who are frequently absent from school who may have different physical activity patterns or associations with friendship groups. Moreover, no data were collected on the ethnic group of the participants which is important as the perspectives and experiences of children from different ethnic groups may vary. All qualitative work is subjective and reliant on the researchers' interpretation of the data  but we attempted to minimize this issue by having two researchers code the data. Moreover, the Moderator and Assistant Moderator wrote up notes from focus groups within 24 hours to prevent deterioration of any key recollections.