Accuracy of consumer-based activity trackers as measuring tool and coaching device in breast and colorectal cancer survivors.

Purpose: Consumer-based activity trackers are used to measure and promote PA. We studied the accuracy of a wrist- and waist-worn activity tracker in cancer survivors and compared these results to a healthy age-matched control group.

Methods: Twenty-two cancer survivors and 35 healthy subjects wore an activity tracker at the waist and at the wrist combined with a reference activity monitor at the waist (Dynaport Movemonitor). The devices were worn for 14 consecutive days. The mean daily step count from both activity trackers was compared with the reference activity monitor to investigate accuracy and agreement (paired t-test, intraclass correlation, Bland-Altman plots). To evaluate the accuracy as a coaching tool, day-by-day differences within patients were calculated. The Kendall correlation coefficient was used to test the consistency of ranking daily steps between the activity trackers and the reference activity monitor.

Results: The wrist-worn wearable significantly overestimated the daily step count in the cancer group (mean ± SDΔ: + 1305 (2685) steps per day; p = 0.033) and in the healthy control group (mean ± SDΔ: + 1598 (2927) steps per day; p = 0.003). The waist-worn wearable underestimated the step count in both groups, although this was not statistically significant. As a coaching device, moderate (r = 0.642-0.670) and strong (r = 0.733-0.738) accuracy was found for the wrist- and waist-worn tracker, respectively, for detecting day-by-day variability in both populations.

Conclusion: Our results show that wrist-worn activity trackers significantly overestimate daily step count in both cancer survivors and healthy control subjects. Based on the accuracy, in particular, the waist-worn activity tracker could possibly be used as a coaching tool.