Background: It has been evident that there is a sharp 
decline in participation in physical activity for adolescent 
girls. Using social cognitive theory as a theoretical 
framework, this study was designed to examine the 
relationships between several psychosocial constructs and 
physical activity levels in adolescent girls, as well as their 
differences across several ethnicities. 
Methods: Participants were 92 sixth through ninth grade 
girls recruited from four urban schools. All girls’ 
psychosocial
 correlates 
(self-efficacy,
 outcome 
expectancy, and social support) were measured and used 
to predict their physical activity levels as measured by 
W4L Neo II pedometers (mean steps per day and mean 
time spent in Moderate to Vigorous Physical Activity 
[MVPA]).  
Results: Girls’ self-efficacy emerged as the sole predictor 
of their mean steps (β = .36, p < .01) and mean time in 
MVPA (β = .38, p < .01). However, girls’ outcome 
expectancy and social support failed to predict physical 
activity levels. Additionally, White girls had more daily 
steps and daily physical activity time than the African
American girls did.  
Conclusion: Adolescent girls’ self-efficacy appeared as 
the only predictor of their daily physical activity levels,  and therefore interventions to enhance their self-efficacy 
should be considered.