Validity of commercially available smartwatches when estimating energy expenditure

Metabolic rate is an energy quantity. Its value is a key input not only in thermophysiological models, but also in the calculation of heat stress indices or complex models predicting a person's thermal sensation. With the dynamic development of technology, sporttesters are able to estimate energy expenditure, among other things. It is a non-invasive method of estimating energy expenditure, or metabolic rate, using associated body functions to predict it. This work deals with the validity of the accuracy of metabolic rate estimation using the Garmin Fenix 6X Pro sporttester in comparison with indirect calorimetry. The accuracy of the metabolic rate estimation was tested for the activities of lying down, administrative work and cycling with regulated mechanical resistance of 100 and 150 W. 15 male subjects aged 28 ± 5 years, with a weight of 83.2 ± 13.5 kg and a height of 180 ± 7 cm participated in the study. In terms of the results, it is possible to observe a lower accuracy of prediction of metabolic rate for low-intensity activities, with the resulting MAPE being around 19-43 %. On the other hand, for activities with moderate activity, the prediction of the metabolic rate by the used sporttester proved to be sufficiently accurate, with a resulting MAPE in the range of 6–8 %