Jf. Sallis et al., Potential mediators of change in a physical activity promotion course for university students: Project GRAD, ANN BEHAV M, 21(2), 1999, pp. 149-158
purpose of the study is to evaluate the performance of theoretically-derive
d mediators of health behavior change. Participants were university seniors
(184 females; 154 males) randomly assigned to an intervention course desig
ned to promote physical activity or to a control course. Five physical acti
vity outcomes and nine psychosocial mediating variables were assessed at ba
seline and the end of the 16-week course. For women, the intervention had s
ignificant effects on five of the mediators, including self-efficacy for ma
king time, self-efficacy for resisting relapse, social support from friends
, and experiential and behavioral processes of change. Among men, the inter
vention improved use of behavioral processes of change but also had the uni
ntended effect of increasing perceived barriers to activity. For women, sig
nificant contributors to regressions explaining physical activity change we
re social support from friends (for total activity) and change in self-effi
cacy for resisting relapse (for vigorous exercise). For men, significant ex
planatory variables included change in enjoyment (for total activity), chan
ge in self-efficacy for resisting relapse (for strength exercise), and chan
ge in benefits (for moderate intensity activity). For both sexes, there wer
e significant findings in the unexpected direction. Across the five physica
l activity outcomes, hypothesized mediators were inconsistent and weak cont
ributors to the models. Investigating mediators of behavior change has the
potential to stimulate improvements in theories and interventions.