Exogenous ingestion of alkalising agents, such as sodium bicarbonate (SB), has been shown to enhance muscle buffering capacity, thereby delaying the metabolic acidosis associated with high-intensity exercise and potentially improving performance. Aim: The aim of this research was to examine the effects of acute and chronic SB supplementation and a placebo (PLA) on high-intensity intermittent performance, recovery and subsequent performance in trained rugby union players. Methods: This aim was achieved through the completion of three interconnected studies. Study 1 examined the effects of acute versus chronic SB supplementation on high-intensity intermittent performance as assessed by 6 x 10s maximal sprint tests on a cycle ergometer. Study 2 investigated effects of chronic SB supplementation on a specifically designed field-based, highintensity intermittent rugby sevens-specific protocol. Study 3 evaluated the effects of acute SB supplementation on an 80-minute high-intensity intermittent 15-a-side rugbyspecific protocol using elite females and sub-elite males. Results: In Study 1, acute SB supplementation demonstrated significant elevations in pre exercise levels for blood bicarbonate (StdHCO3 -), pH and base excess (BE-Ecf) but no significant improvement in peak power output (PPO), mean power output (MPO) or total work (TW). Chronic SB supplementation exhibited a significant increase in StdHCO3 - following Sprint 1. However, no significant differences in performance parameters were recorded for either acute or chronic SB supplementation when compared to the PLA trial. In Study 2, no significant differences in blood or performance related variables were observed between chronic SB and PLA supplementation trials. In Study 3, pre-exercise alkalosis was induced by acute SB supplementation in both elite females and sub-elite males. However, this did not translate into an ergogenic benefit to rugby union-specific performance. Vertical jump height and passing accuracy were significantly improved with PLA as opposed to SB supplementation in the elite female group. No significant differences in performance were observed between trials in the sub-elite male group. Conclusion: The major findings of this work suggest that pre-exercise metabolic alkalosis may be induced following acute but not chronic SB ingestion. However, results are inconclusive regarding the efficacy of acute or chronic SB ingestion to enhance performance in high intensity, intermittent performance indicative of the movement patterns and physiological demands associated with rugby union. Results also appear to indicate a high degree of individual variability, which, in part, may be due to potential gastrointestinal side effects of SB ingestion.