The Withings smartwatch showed minimal systematic bias for resting heart rate assessment but demonstrated systematic underestimation of step counts with wide limits of agreement compared with a research-grade accelerometer in children and adolescents undergoing cancer treatment.
The Withings smartwatch recorded significantly fewer steps per hour than the ActiGraph accelerometer in children and adolescents with cancer.
The Withings smartwatch recorded significantly fewer steps per day than the ActiGraph accelerometer.
No statistically significant difference in resting heart rate was observed between the Withings smartwatch and a clinical heart rate monitor.
Individual variability in resting heart rate measurement was considerable despite minimal systematic bias.
The study population consisted of children and adolescents aged 8 to 18 years under active cancer treatment.
The use of smartwatch-derived step counts for clinical benchmarking or goal setting in children and adolescents undergoing cancer treatment cannot currently be recommended.
This research suggests that a consumer smartwatch (Withings) can reliably measure resting heart rate in children and teenagers receiving cancer treatment, but significantly underestimates how many steps they take compared to a research-grade activity tracker. The study enrolled 14 young patients aged 8–18 who wore both devices simultaneously — the smartwatch alongside an ActiGraph accelerometer for step counting, and alongside a clinical heart rate monitor for heart rate comparisons. On average, the smartwatch counted about 3,154 fewer steps per day than the research device, and this gap grew larger as activity levels increased, meaning the more active the child, the more steps the smartwatch missed. For heart rate at rest, however, the smartwatch was only off by about 1 beat per minute on average, though individual readings could vary by as much as 17 beats per minute in either direction. This matters because smartwatches are increasingly being considered as tools to help monitor and encourage physical activity during childhood cancer treatment, which is a period when maintaining activity can support recovery and quality of life. This research suggests that while a smartwatch may be adequate for tracking resting heart rate trends, its step count data should not be used for setting clinical activity goals or benchmarking patient progress against established norms, as the systematic undercount and wide individual variation could lead to inaccurate conclusions about how active a child is during treatment.
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Upload Your Labsden Hartog E, Fiocco M, van der Torre P, Tissing W, Verwaaijen E. (2026). Monitoring Steps and Heart Rate Using a Withings Smartwatch in Children and Adolescents With Cancer: Validation Study.. JMIR cancer. https://doi.org/10.2196/77766