Wearables for health and fitness: Measurement characteristics and accuracy

To date, wearable devices are increasingly widespread among different kinds of users (e.g. sport people, patients, but also young and adult people in general) to monitor physiological parameters (e.g. heart rate, skin temperature, steps and energy expenditure), depicting the subject's physical activity pattern during different activities. Nonetheless, an insufficient attention is paid to the measurement characteristics and the accuracy of these devices, which, on the contrary, are of utmost importance, especially if the wearable is used for health or fitness purposes since uncertainty affects the result itself. The aim of this work is to analyze the performances of wearable devices and the measurement procedure used to validate them with respect to gold standard instruments, such as electrocardiogram for cardiac parameters or calorimetry for energy expenditure. What clearly appears is the lack of a standard test protocol in the validation process, as well as a large variability in the expression of metrological characteristics of this class of measurement device (e.g. referring to accuracy, some authors use bias, others absolute error). Therefore, in the field of wearable devices research it would be fundamental to identify some common measurement parameters and to devise a kind of guidelines, in order to obtain repeatable and inter-comparable data that can be reliably compared.