Heart Rate Monitor Agreement in Breast Cancer Survivors in A Community-based Exercise Program

Appropriate exercise intensity, often expressed as target heart rate (HR), is critical to effecting change in symptom burden in breast cancer survivors (BCS). Traditional chest-worn monitors, despite their well-documented validity, may be inconvenient in unsupervised settings due to necessary receivers and participant discomfort. Commercially-available wearable sensors may represent an accessible alternative to HR monitoring in community-based exercise settings. PURPOSE: To examine the agreement between the Fitbit Inspire HR and Polar chest monitor for HR measurement in BCS at different stages of exercise in a community-based program. METHODS: BCS (N = 9; aged 38-72 years) were randomized to a 12-week moderate intensity (45-75% HR reserve) pilot aerobic exercise program. HR was concurrently measured using a Polar chest strap monitor and wrist-worn Fitbit Inspire HR in 5 stages: pre-exercise seated rest; midpoint of a 5-minute warmup; midpoint of moderate intensity exercise; midpoint of a 5-minute cool-down; after a 5-minute seated recovery. Agreement between HR measurements was assessed using Lin’s concordance correlation coefficient (rc). Relative error rates were calculated to indicate differences across exercise session stages. RESULTS: Across sessions (n = 187), HR ranged from 55 to 139 beats per minute. Agreement between the Polar monitor and Fitbit Inspire HR was highest during seated rest (pre-exercise, rc = 0.74, 95%CI [0.67, 0.80]; post-exercise, rc = 0.90, 95%CI [0.86, 0.92]) followed by the midpoint of moderate intensity exercise (rc = 0.63, 95%CI [0.54, 0.70]). Agreement was lowest during “transitionary” periods—i.e., warmup (rc = 0.37, 95% [0.25, 0.49]) and cool-down (rc = 0.43, 95% [0.32, 0.53]). Mean relative error rates ranged from -4.30% to 3.27% and were greatest during the warmup stage (RER = -4.3 ± 12.06%). CONCLUSION: This study provides novel data on HR monitor agreement in a community-based exercise setting and in a clinical population. Results indicate moderate agreement between Fitbit Inspire HR and Polar HR monitors during steady-state, moderate intensity aerobic exercise. While Fitbit alone may provide an estimate of exercise HR, it is likely not precise enough for accurate HR monitoring in exercise prescription.