Background: Recent reports suggest that the use of non-contact mouthpieces may be beneficial at improving aerobic and anaerobic exercise performance.However, the mechanisms of these reported improvements have yet to be elucidated. The purpose of this study was to explore the possible mechanisms of improved performance using the ArmourBite® mouthpiece (UnderArmor, Baltimore, Maryland). Methods: Using a within subject randomized treatment design, 15 advanced resistance trained males (19-26 years of age) performed 6 sets of 10 repetitions of free weight back squats at 80% of 1RM with and without a mouthpiece. Blood samples were collected (indwelling venus catheter) before exercise, after 3 sets (Mid), immediately post (Post), 30 minpost (Post-30), 60 minpost (Post60) and 120 minpost (Post-120) exercise.Samples were analyzed for lactate (Lactate Plus, Waltham, MA) and ELISA was used to determine cortisol. Results: Mouthpiece use resulted in more repetitions completed without assistance (54.36 ± 0.61 vs. 53.27 ± 0.79, p< 0.05) and fewer forced repetitions (6.73 ± 0.79 vs. 5.64 ± 0.61 repetitions, p< 0.05) compared to the control group. Lactate concentrations were lower in the treatment versus control group at the Post (11.54 ± 2.23 vs. 13.07 ± 2.96 mmol/L, p< 0.05), Post-30 (4.45 ± 1.94 vs. 5.41 ± 1.90 mmol/L, p< 0.05), and Post-60 (2.07 ± 0.94 vs. 2.55 ± 0.96 mmol/L, p< 0.05) sampling periods. Mouthpiece use lowered cortisol levels at Mid and Post-30 (19.39 ± 6.90 vs. 27.84 ± 14.56 µg/dL, p< 0.05; 22.91 ± 8.47 vs. 31.81 ± 10.79µg/dL, p< 0.05). Cortisol AUC values showed significant differences within the AUC pre-post control and treatment (55.16 ± 23.84 vs. 41.95 ± 2.65 µg/dL, p< 0.05) groups. Conclusion: These data suggest that mouthpiece use may increase performance and decrease stress when used during intense resistance exercise.