Despite the prevalence of wearable technology devices that claim to track various aspects of exercise, like heart rate (HR) or energy expenditure (EE), few companies have independently had their products tested. Thus, there is a need to measure validity and reliability of wearable technology devices in any situation a consumer may use them, like aerobic or resistance exercise training. PURPOSE: To determine the validity and reliability of the bicep worn Polar Verity in measuring average and maximal HR and estimated EE during light circuit resistance training. METHODS: Twenty subjects (n=10 female and male; age: 23.27.7 years; height: 169.711.1; weight: 76.315.7 kg) completed this study. Bicep worn Polar Verity device was evaluated, along with the Polar H10 chest strap and Cosmed K5 portable metabolic unit as the criterion devices for average HR and EE, respectively. Subjects completed 4 circuits of 4 exercises (front squat, reverse lunge, push-ups, and shoulder press) using dumbbells at a light intensity with 1 set of 10 repetitions per exercise, 30 seconds rest between exercises, and 1-1.5 min. rest between circuits. Data were analyzed for validity (Mean Absolute Percent Error [MAPE] and Lin's Concordance Coefficient [CCC]) and reliability (Coefficient of Variation [CV]), with predetermined thresholds of MAPE<10%, CCC>0.70, and CV<10%. A paired t-test was used to determine differences (p<0.05). RESULTS: Polar Verity was significantly (p<0.0001) different than the Cosmed K5 for EE in kcals (46.4±16.5 versus 20.3±5.5 kcals, respectively) with a MAPE of 503.7%, Lin's Concordance of -0.00, and CV of 12.2%. Conversely, the Polar Verity was not significantly (p>0.05) different than the Polar H10 for either average HR (127.4±19.2 versus 128.9±19.0 bpm, respectively) or maximal HR (145.7±19.1 versus 145.8±18.2 bpm, respectively). Further, for average HR and maximal HR the Polar Verity MAPE was 7.0% and 5.7%, respectively, Lin's Concordance was 0.98 and 0.98, respectively, and CV was 0.6% and 0.5%, respectively. CONCLUSION: The bicep-worn Polar Verity was valid and reliable for average HR and maximal HR, but was neither valid or reliable for estimated EE during light resistance training. Consumers should be aware of the energy expenditure limitation of this bicep worn device when performing resistance training.