Caloric Expenditure Using Indirect Calorimetry, Apple Watch Sport, and Fitbit Zip

Document Type

Article - Open Access

Publication Title

Journal of Exercise Physiology


American Society of Exercise Physiologists

Publication Date


Abstract/ Summary

The aim of this study was to compare caloric expenditure values during exercise using Apple Watch Sport, Fitbit Zip, and indirect calorimetry. The study included 7 healthy subjects (3 men and 4 women). The subjects completed six 6-min bouts of sitting, treadmill walking, and jogging (sitting, 4.0, 5.6, 6.8, and 8.9 km·hr-1 , followed by 4.0 km·hr-1 cool-down) while wearing an Apple Watch Sport and a Fitbit Zip. Oxygen consumption (VO2) was measured using the Cosmed Quark CPET. The data were analyzed using ANOVA (P<0.05). The results are presented as means ± SD. Caloric expenditure values for the Fitbit Zip were significantly higher than values calculated from VO2 for all walking and jogging speeds (P<0.05). In contrast, caloric expenditure values for Apple Watch Sport were not significantly different than values calculated from VO2 (P>0.05). Total caloric expenditure values were also significantly higher for the Fitbit Zip (296.3 ± 33.0 kcals) compared to values calculated using VO2 (195.8 ± 30.4 kcals) and the Apple Watch Sport (201.1 ± 41.5 kcals) (P<0.05). The results of this study suggest that the Fitbit Zip may overestimate caloric expenditure compared to indirect calorimetry. In contrast, caloric expenditure values from the Apple Watch are not different from the indirect calorimetry values. This information may be important for exercise professionals to consider when recommending physical activity trackers to clients.