The purpose of this study was to assess the validity of the ActiGraph GT3X+ (GT3X+) and the BodyMedia SenseWear Armband (SWA) to estimate energy expenditure (EE) during physical activity and field sport movements.Criterion validity.Twenty-six active adults completed a single 90min session involving alternating intervals of exercise (5min) and recovery (10min). Exercise involved walking (4km/h), jogging (8km/h), running (12km/h) or a sport-simulated circuit (three intervals). Participants wore two triaxial accelerometers (GT3X+ and SWA) and a portable gas analyser (MetaMax 3B), used as the criterion measure.Total EE was significantly underestimated (p<0.01) by the GT3X+ (mean bias±SD: -374.5±132.84kJ; % difference=-29.3%) and SWA (-244.3±148.0kJ; -18.2%). Overestimations were made by both accelerometers during the walk (GT3X+: 27.4±30.8kJ; SWA: 32.1±15.4kJ) and jog (38.0±30.0kJ; 34.5±31.6kJ). Underestimations were evident during the run (-41.2±25.1kJ; -43.8±33.5kJ) and circuit (C1: GTX+: -127.2±41.6kJ; SWA: -86.1±40.2kJ). Error of estimation increased in magnitude as the intensity of exercise increased (GT3X+: 40.8-143.0kJ; SWA: 35.5-102.0kJ).The ActiGraph GT3X+ and BodyMedia SWA do not provide valid EE estimates across a range of exercise modalities and intensities when compared to a criterion measure. Poor accuracy and large precision errors, particularly during high intensity and intermittent movement patterns, suggest these devices have limitations and should be used cautiously in the field.