These results confirm direct and indirect relations between self-efficacy and physical activity, consistent with hypotheses from self-efficacy theory about the functional network of efficacy beliefs with perceived social support, self-management, and perceived barriers to physical activity. Self-efficacy had a direct relation with physical activity and an indirect relation with physical activity that operated through an inverse relation with perceived barriers. Although derived from a longitudinal design, the hypothesized relations we tested between physical activity and the social-cognitive variables are cross-sectional and do not permit inferences about the cause.
Although perceived social support was related to physical activity in the 6th grade, independently of self-efficacy and the other social-cognitive variables, it did not have a direct relation with physical activity in the 8th grade. Rather, it had a weak indirect relation that was mediated through its inverse relation with perceived barriers. Consistent with theory, that relation was moderated by self-efficacy for overcoming barriers to physical activity. Girls who perceived low social support perceived more barriers to physical activity than girls who perceived high social support but only if they also had low self-efficacy.
Previous studies showed that perceived support from family (Dowda et al., 2007
; Kuo, Voorhees, Haythornthwaite, & Young, 2007
; Neumark-Sztainer et al., 2003
) and friends (Duncan, Duncan, & Strycker, 2005
) each is related to physical activity among adolescent girls, so a focus of the present study was to determine whether those relations were stable between the 6th and 8th grades and independent of other social-cognitive variables, specifically self-management strategies and perceived barriers. Results were the same when the model included family support or friend support subscales, with the exception that perceived friend support was not related to perceived barriers in the 8th grade. That result is understandable given the increasing reliance of girls in early adolescence on parents and older siblings for the provision (e.g., transportation) of opportunities for physical activity outside of school. Because perceived support from family members and friends appears to be a stronger influence on physical activity among adolescent girls than is a subjective social norm (Saunders, Motl, Dowda, Dishman, & Pate, 2004
), future research should examine mechanisms by which social support is provided (e.g., Dishman, Saunders, et al., 2009
; Duncan et al., 2005
) and whether commonly used measures of social support of physical activity operate as proxy measures of social networks (Voorhees et al., 2005
) or social incentives for physical activity among girls.
Only perceived social support changed between the 6th and 8th grade measurements; the mean scores were lower in the 8th grade. That change was unrelated to whether girls were assigned to the intervention or control arms of TAAG. Likewise, the group assignment was unrelated to initial status or change scores for physical activity and the other social-cognitive variables. In the absence of a mean change in a variable, heterogeneity in difference scores between two assessments can reflect unreliability across time rather than a true change (Duncan et al., 2006
). Hence, the analysis we used in this study exploited the longitudinal nature of the data to provide unbiased parameter estimates in the 8th grade by accounting for inter-individual heterogeneity in initial status (i.e., 6th grade scores) and change (i.e., differences between 6th and 8th grade scores), as well as unmeasured common causes among the variables assessed in the 6th grade.
A novel feature of the study was the use of an objective measure of physical activity. Aside from eliminating concerns about inflated relations between physical activity and girls’ beliefs biased by a common method of self-report, the use of accelerometry has the advantage of assessing both intensity and duration of physical activity. Thus, we were able to estimate the volume (intensity × duration) of moderate-to-vigorous physical activity (Treuth et al., 2004
), rather than merely the frequency of activity as has been done in similar large-scale studies (Going et al., 2003
; Sallis, McKenzie, Alcaraz, Kolody, Faucette, & Hovell, 1997
Although hypothesized relations of social-cognitive variables with physical activity were supported, the associations were not as strong as expected (Sallis, Taylor, Dowda, Freedson, & Pate, 2002
), suggesting that previous estimates have been inflated by a common method artifact of self-report (Dishman, 1994
). The magnitude of the direct and indirect relations between self-efficacy and physical activity approximated .14 SD
, which is small when judged by conventional standards for sample statistics (Cohen, 1988
). However, when judged as a binomial effect (Rosenthal & Rubin, 1982
), the practical impact of a relation of this size approximates an effect of 3–4% above a control rate, hypothetically facilitating the physical activity of about 35 girls in this sample.
Another novel feature of the study was the multi-ethnic cohort of girls from six regions of the United States. White girls had higher initial levels of self-efficacy and perceived social support and reported greater use of self-management strategies than the other girls, but only change in perceived social support was related to race/ethnicity; Hispanic/Latino girls reported a larger decline than White girls. Physical and cultural (i.e., socio-cultural milieus that differ in shared values, customs, and social practices) environments might have a stronger relation with physical activity than perceived social environments specific to physical activity (Bandura, 1997
), particularly among adolescent girls of African American or Hispanic descent (e.g., Wilbur, Chandler, Dancy, Choi, & Plonczynski, 2002
). Nonetheless, the relations among variables that we report are independent of the race or ethnicity reported by the girls, and they are independent of any differences observed in the variables among the six field sites. Results might be different among non-English speaking girls. Research is needed to determine whether socio-economic status moderates social-cognitive influences on girls’ physical activity independently of their race/ethnicity.
Studies using different measures have reported change in girls’ barriers self-efficacy across shorter time periods (Duncan et al., 2007
; Neumark-Sztainer et al., 2003
). However, those reports did not establish the measurement equivalence/invariance of the questionnaires to insure that the same construct was being measured at each time, which is necessary for the proper interpretation of change in tests of mediating relations (
Mackinnon et al., 2007
). When viewed with our past findings of stable self-efficacy during high school (Dishman, Saunders, et al., 2009
), the present results suggest that, in the absence of effective intervention (e.g., Dishman et al., 2004
; Edmundson et al., 1996
), girls’ self-efficacy about overcoming barriers to physical activity is mainly formed by the 6th grade. If so, physical activity interventions to enhance self-efficacy might be needed before adolescence.
A large-scale intervention conducted on elementary school students reported increases in self-efficacy and perceived social support and an increase in self-reported physical activity that was sustained through the 8th grade (Edmundson et al., 1996
; Nader et al., 1999
; Parcel, Simons-Morton, O’Hara, Baranowski, & Wilson, 1989
). However, it was unclear from reports on those studies whether initial levels or changes in self-efficacy and perceived social support were directly or indirectly related to physical activity at the level of the students. Also, the longitudinal measurement equivalence/invariance of the measures was not established, preventing a clear conclusion that the change in scores reflected a true change in their underlying constructs.
A secondary aim of TAAG was to affect positive changes in the putative social-cognitive mediators of change reported on here, but incomplete implementation of some features of the intervention likely mitigated attainment of some secondary outcomes (Young et al., 2008
). A smaller observational study of changes in physical activity beliefs across the elementary to middle school transition reported that girls had a decrease in perceptions of social support for physical activity and were less likely to perceive that the benefits of regular activity out-weighed the barriers (Garcia, Broda, Frenn, Coviak, Pender, & Ronis, 1995
). Consistent with our present findings based on an objective measure of physical activity, self-reported physical activity in that study did not change.
We recommend that future research on social-cognitive influences on physical activity include features of the cultural environment, account for parental education and income, and add objectively measured features of the physical (e.g., Dowda, Dishman, Porter, Saunders, & Pate, 2009
) and social environments in racially or ethnically diverse samples of adolescent girls and boys.