Subjective reporting about healthy behaviors results in data that are shaky at best and outright wrong and misleading in the worst cases. A metastudy of medical adherence at Johns Hopkins Bloomberg School of Public Health published in 2014 found patient noncompliance ranged from 25% to 50%. Even with serious illness — when adherence to a routine or regimen has a direct correlation with recovery or quality of life — compliance and positive outcomes are much more likely when objective tracking is possible. In 2016 researchers at the Memorial Sloan Kettering Cancer Center found that subjective measures used by physicians to assess a cancer patient’s fitness were also ineffective. This has important ramifications in terms of the patient’s ability to tolerate different forms of treatment.

A recent study at Cedars-Sinai Medical Center in Los Angles showed that wearable activity monitors were effective in objective assessment of patient performance status (PS). Thirty-seven patients with advanced stage cancers wore off-the-shelf Fitbit Charge HR fitness wristbands. The wearables monitored and reported continuous heart rate data, all-day activity tracking, sleep time, and sleep stages. The study authors correlated the objective physical activity measurements with clinical outcomes during a 6-month period and found positive relationships between the Fitbit-reported metrics and physical functioning, pain, fatigue, and emotional distress. For example, for every increase of 1,000 steps per day increase, there was a corresponding reduction in the chances of adverse events. The activity reporting, particularly steps, also correlated with patient-reported outcomes (PROs). While the report authors stopped short of suggesting that the Fitbit Charge HR could replace traditional patient fitness and functionality assessments, they confirm that the trackers were effective supplementary tools and provided more detailed and continuous accounting of the patients’ activity levels.

The study authors called for additional testing with larger and more heterogeneous groups to validate their observations. They also stated that, while device validation is always an issue, the Fitbit Charge HR has been validated for clinical use and that the accuracy of new wearable activity monitors will continue to improve. This study points to some of the medical benefits that can be derived from data generated by common, off-the-shelf consumer wearable devices, and we can expect more uses like this in the future.