INTRODUCTION: Exercise is pursued by healthy, clinical and athletic populations and unquestionably, plays a pivotal role in health and wellbeing and the advancement of athletic performance. The ability to exercise at higher intensities provides a greater stimulus for cardio-pulmonary, metabolic, neuromuscular and musculoskeletal adaptations but is compromised by fatigue-limiting symptoms, both physiological and psychological, the mechanisms underpinning which are not completely understood. Recent advances in our understanding of fatigue mechanisms have identified respiratory system limitations and the potential for respiratory adaptation. Individual breathing patterns exist, functional and dysfunctional, influenced genetically, developmentally and by multiple psychophysiological mechanisms but importantly it exhibits considerable plasticity. Advances in neuroscience, have identified the potential for respiratory neuroplasticity and its’ bi-directionality, with meditation style activities which incorporate deep breathing showing both functional and structural changes in neural structures and circuitry. Differences between athletes and non-athletes and males and females in both pattern and response to exercise exist. Little research has focused on the manipulation of breathing patterns which can potentially influence physiological and psychological factors in fatigue mechanisms. AIM: To investigate if adopting a deep breathing pattern during exercise can improve exercise performance via effects on gas exchange parameters and/or perceived exertion. MEHODS: Three studies examined the effect of a self-regulated, deep breathing pattern on exercise performance. Study 1 examined constant work rate (CWR) heavy intensity exercise in a heterogenous group of healthy males and females, untrained and trained runners. Study 2 assessed endurance running performance, via a lab-based maximal, incremental vVO2peak treadmill running test. Study 3 examined the effect on high intensity interval exercise (HIIE) performance via a lab-based, treadmill interval running test to exhaustion. RESULTS: Study 1 showed a significant improvement in locomotor efficiency as observed by reductions in both oxygen cost and energy cost. Study 2 and Study 3 showed no significant difference in performance measures. CONCLUSION: Deep breathing improves locomotor efficiency in CWR, heavy intensity locomotion. No significant benefit was observed on running performance or HIIE performance in healthy male endurance athletes.