Levels and patterns of self‐reported and objectively‐measured free‐living physical activity among prostate cancer survivors: A prospective cohort study

BACKGROUND: No prior study has measured or compared self‐reported and objectively measured physical activity trajectories in prostate cancer survivors before and after treatment. METHODS: Clinically localized prostate cancer patients treated with radical prostatectomy were recruited between 2011 and 2014. Of the 350 participants enrolled at the main site, 310 provided self‐reported physical activity at baseline before radical prostatectomy, and 5 weeks, 6 months, and 12 months after radical prostatectomy. A subset of participants (n = 81) provided objectively measured physical activity at all study time points by wearing an accelerometer for 7 days each. Changes in activity over time were compared using Friedman’s test. Agreement between self‐reported and objective measures was evaluated using Spearman’s rank correlation coefficient. RESULTS: Self‐reported moderate‐to‐vigorous physical activity was high at baseline (median, 32.1 min/day), followed by a decline at 5 weeks (median, 15.0 min/day) and a recovery at 6 and 12 months (median, 32.1‐47.1 min/day). In contrast, objectively measured moderate‐to‐vigorous physical activity was low at all 4 time points (median, 0.0‐5.2 min/day), with no overall change across study assessments (global P = .29). Self‐reported moderate‐to‐vigorous physical activity tended to be more closely related to objectively measured light‐intensity physical activity (ρ = 0.29‐0.42) than to objectively measured moderate‐to‐vigorous physical activity (ρ = 0.07‐0.27, P = .009‐.32). CONCLUSIONS: In our population of prostate cancer survivors with critically low moderate‐to‐vigorous physical activity levels, self‐reported measures greatly overestimated moderate‐to‐vigorous physical activity and may have been more reflective of light‐intensity physical activity. Because cancer survivor guidelines are derived from self‐reported data, our findings may imply that intensities of physical activity below moderate, such as light intensity, still have health benefits.