Estimation of physical activity intensity cut-points using accelerometry in breast cancer survivors and age-matched controls.

OBJECTIVE: To examine the association between accelerometer activity counts and energy expenditure during walking in breast cancer survivors (BCS) compared with age-matched healthy controls, and differences in moderate-to-vigorous physical activity (MVPA) cut-points.

METHODS: Using a case-control design, 19 BCS and 19 age-matched women completed 6 min of resting energy expenditure and 6-min periods of treadmill walking in Midwestern United States. Accelerometers and an open-circuit spirometry system were used to measure activity counts and energy expenditure (VO2 ). A mixed-factor analysis of variance was conducted on activity counts and VO2 . Independent samples t tests compared the magnitude of associations between groups.

RESULTS: There were group by speed interactions on energy expenditure (p < 0.001) and counts (p < 0.001). The linear association did not differ between BCS and controls for the R2 (p = 0.62) nor the slope (p = 0.43), but there was a difference in the intercept (p = 0.01). This resulted in different MVPA cut-points between groups: 1,439 ± 761 counts·min-1 in BCS and 1,937 ± 639 counts·min-1 in controls.

CONCLUSION: The findings support the use of different cut-points to quantify time spent in MVPA for BCS. Application of these cut-points is warranted to accurately assess physical activity (PA) patterns for better prescription and health outcomes in PA programmes for BCS.