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. 2025 Nov 27.
doi: 10.1007/s11764-025-01943-w. Online ahead of print.

Predictive ability of the theory of planned behavior on physical activity in newly diagnosed women with breast cancer: a prospective cohort study

Chad W Wagoner  1 , Christine M Friedenreich  2   3 , Kerry S Courneya  4 , Qinggang Wang  5 , Jeff K Vallance  6 , Charles E Matthews  7 , Lin Yang  2   5   3 , Margaret L McNeely  8 , Leanne Dickau  5 , S Nicole Culos-Reed  2   9   10
Affiliations

Predictive ability of the theory of planned behavior on physical activity in newly diagnosed women with breast cancer: a prospective cohort study

Chad W Wagoner et al. J Cancer Surviv. .

Abstract

Purpose: Few studies assess how well the Theory of Planned Behavior (TPB) predicts physical activity over time after a breast cancer diagnosis. This study evaluated TPB's prediction, measured at diagnosis, on women's physical activity 1 year later.

Methods: The Alberta Moving Beyond Breast Cancer (AMBER) study follows women recently diagnosed with breast cancer (n = 1528; average age 55.4). Participants completed questionnaires on TPB variables about recreational activity shortly after diagnosis. At 1 year, actiGraph GT3X+® devices measured light and moderate-vigorous activity, and self-reported activity over the past year was assessed with the Past Year Total Physical Activity Questionnaire. Structural equation models evaluated TPB variables' ability to predict physical activity after 1 year.

Results: At diagnosis, positive attitudes (β = 0.51; p < 0.001) and greater perceived behavioral control (β = 0.16; p < 0.001) were associated with greater intentions for physical activity derived from device-measured (R2 = 0.51, p < 0.001) and self-reported questionnaire (R2 = 0.54, p < 0.001). The TPB at diagnosis was associated with greater device-measured MVPA at 1 year (β = 0.13; p < 0.01). The TPB was not associated with device-measured light-intensity physical activity (β = 0.07; p = 0.08) or self-reported recreational physical activity (β = 0.08; p = 0.07).

Conclusion: The variance explained by the TPB for physical activity at 1 year after breast cancer diagnosis was minimal. These findings highlight the need to identify additional factors influencing intentions and long-term activity.

Implications for cancer survivors: Incorporating behavior change strategies that influence attitudes toward physical activity may positively impact intentions at diagnosis. To ensure long-term activity among breast cancer survivors, supportive care should include interventions addressing factors beyond initial intentions.

Keywords: Breast cancer; Intention-behavior gap; Physical activity; Structural equation modeling; Theory of Planned Behavior.

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Conflict of interest statement

Declarations. Ethics approval: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Informed consent: The Health Research Ethics Board of Alberta: Cancer Committee (HREBA.CC-17-05076) granted approval. Informed consent was obtained from all participants included in the study. Conflict of interest: The authors declare no competing interests.

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