Introduction The continuous quantification of free-living energy expenditure (EE) would be critical to the study of energy balance and obesity. Wearable activity monitoring devices are increasingly prevalent in research environments for the estimation of EE and heart rate (HR), creating new opportunities for long-term free-living measurements. The aim of this study was to validate the accuracy of HR and EE estimates of the Fitbit charge 2 (FC2), and the EE estimates of a research-grade accelerometer, the Sensewear armband mini (SWA). Methods We recruited 59 healthy adults (age = 44.42 ± 14.14 years, body weight = 75.65 ± 13.63 kg). Participants performed a physical activity protocol including walking, running, cycling, sedentary and household tasks. Estimates of HR were compared to a HR chest strap (Polar) and EE to a stationary metabolic cart (Vyntus CPX). Results Overall, the SWA overestimated EE by of 0.02 kcal/min-1 and was statistically equivalent to the criterion measure, with a mean absolute percentage error (MAPE) of 29.37%. In contrast, the FC2 was not equivalent overall (MAPE = 44.17%). In household tasks, MAPE values of 93% and 83% were observed for the FC2 and SWA, respectively. The FC2 HR estimates were equivalent to the criterion measure overall and for all tasks except ambulation (flat and incline) and cycling (low and moderate intensities). Conclusions The SWA is more accurate than the commercial-grade FC2 and neither device is consistently accurate across the range of activities used in this study. The HR data obtained from the FC2 is more accurate than its EE estimates and future research may focus more on this variable.