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.