Background: The studies show low level of physical activity among girls in different societies. Moreover, there are some cultural barriers for Iranian women exercising in public places. In addition, physical activity declines precipitously with increased age among adolescents, especially in girls. Objectives: The aim of this study was to identify the relation between physical activity level and the structures of Trans-theoretical model (TTM). Materials and Methods: This cross-sectional study was conducted on 423 female students of Tonekabon in Iran. Participants completed the demographic questionnaires, the TTM’s structural questionnaires as well as the international physical activity questionnaire short form for assessing the levels of physical activity (IPAQ-SF). Results: The age mean of the students was 15.34±0.67 years. The balance decisional questionnaire (69.19±8.35) and process of change (56.81±12.76) questionnaire received the highest average scores. The majority of the students (67.4%) were at the pre-operational stage (pre- contemplation, contemplation, preparation); while 257(60.8%) of students reported to have light physical activity or no activity. Self-efficacy had the strongest correlation with the levels of physical activity. Conclusions: We identified the self-efficacy structure as the most effective factor of physical activity performance. Thus, enhancing the self- efficacy may be useful in order to promote the practice of physical activity.

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