Objective: The effects of self-efficacy beliefs on physical activity are well documented, but much less is known about the origins of self-efficacy beliefs. This article proposes scales to assess the sources of self-efficacy for physical activity aims and to comparatively test their predictive power for physical activity via self-efficacy over time to detect the principal sources of self-efficacy beliefs for physical activity.

Method: A study of 1,406 German adults aged 16–90 years was conducted to construct scales to assess the sources of self-efficacy for physical activity (Study 1). In Study 2, the scales’ predictive validity for self-efficacy and physical activity was tested in a sample of 310 older German adults.

Results: Short, reliable and valid instruments to measure six sources of self-efficacy for physical activity were developed that enable researchers to comparatively test the predictive value of the sources of self-efficacy.

Conclusion: The results suggest that mastery experience, self-persuasion, and reduction in negative affective states are the most important predictors of self-efficacy for physical activity in community-dwelling older adults.