Polar Activity Watch 200: a new device to accurately assess energy expenditure

Objectives Energy expenditure (EE) based on movement detection is calculated by a new device, the Activity Watch 200 (AW200). The aim of this study was to validate EE measured by this device against indirect calorimetry (IC) and to assess the reproducibility of AW200 measurements. Design EE was assessed during a 9.7 km hike. 10 men and 10 women in the age range 35-45 years, and 5 men and 6 women in the age range 50-55 years were tested. One in five participants of each age-and sex-matched group was equipped with a portable metabograph (Oxycon Mobil) for IC measurements. Data were collected every 30 min during the hike, and IC was extrapolated for the remaining four other participants of the group. Results During the total hike, there was a high correlation between EE obtained from the AW200 and the IC calculation (r = 0.987, p < 0.001). Identical values of EE were calculated by both methods during the first 90 min of the hike. However, EE calculated by the AW200 at 120 min and at the end of the hike was lower (p < 0.05). Bland-Altman analysis showed limits of agreements between 105 and 279 kJ after 30 and 120 min, respectively. EE measured by the AW200 was well correlated with IC measurements, and limits of agreement between devices were below 10% of the measured values for hike durations longer than 60 min. Conclusion The AW200 appears to be a very useful and accurate device for measuring EE during exercise in recreational hikers and provides a useful tool for keeping track of personal EE.