Examining bidirectional longitudinal relationships between physical activity and physical function in older breast cancer survivors: The Thinking and Living with Cancer study.

BACKGROUND

Older breast cancer survivors are susceptible to cancer- and treatment-related losses in physical function that can negatively affect daily living activities, mobility, and independence. Although physical activity can improve physical function, few studies have focused on older survivors or explored interrelationships between physical activity and physical function. Longitudinal bidirectional relationships between physical activity and physical function in breast cancer survivors and noncancer controls aged 60+ years were evaluated.

METHODS

Survivors (aged 67 ± 7 years; n = 357) newly diagnosed with nonmetastatic breast cancer (stages 0-III) and noncancer controls (aged 67 ± 9 years; n = 254) were assessed at baseline (postsurgery and pre-systemic therapy among survivors) and annual visits for up to 36 months. Physical activity (steps per day) was assessed via actigraphy. The Timed Up and Go test (longer time indicates lower function) and 12-item Short Form Health Survey Physical Component Score evaluated physical function. Data were analyzed via random-intercepts cross-lagged panel models, with controlling for covariates; p values of ˂.05 were considered statistically significant.

RESULTS

Starting from the 12-month visit, higher daily steps predicted better subsequent Timed Up and Go time among survivors and controls, and the magnitude of effect was stronger for survivors than controls at 24 months (post hoc comparison, p = .036; survivors: β = -0.420; p = .003; controls: β = -0.211; p = .032). Timed Up and Go time did not predict later daily steps. Associations between steps and the Physical Component Score showed similar patterns.

CONCLUSIONS

Higher daily steps predicted better subsequent physical function, especially in survivors. These results highlight the importance of promoting physical activity during cancer survivorship care to maintain functional independence.