ObjectivesThis study quantified blood bicarbonate (HCO3−) kinetics and gastrointestinal upset to determine the gender-related ergogenic potential of sodium bicarbonate (0.15-, 0.25- and 0.35 gSB·kgFat-free mass (FFM)–1) in high intensity functional training. DesignDouble-blind randomized placebo-controlled crossover. MethodsThirty female and male athletes performed two bouts of the Wingate Anaerobic Test (WAnTPRE-HIFT and WAnTPOST-HIFT) interspaced with two 3-min bouts of Wall Balls and Burpees 120min after ingestion of three sodium bicarbonate doses. Blood HCO3− was determined pre-ingestion, after supplementation and before/post exercise. Gastrointestinal upset was evaluated 120min post-ingestion. Control (CTRL) measurements were performed. ResultsThere were significant gender×treatment interactions for: changes in blood HCO3− at 60min post-ingestion (p=0.014; η2p=0.104; at 0.15gSB·kgFFM−1 males experienced higher increase than females); peak power (p=0.015; η2p=0.103) and average power (p=0.005; η2p=0.124) during WAnTPOST-HIFT, and changes in peak power between the Wingate Anaerobic Test bouts (p=0.049; η2p=0.081). Sodium bicarbonate compared to PLA had no significant impact on Wall Balls and Burpees performance. The dose of 0.35gSB·kgFFM−1 resulted in higher less severe gastrointestinal symptoms compared to CTRL and 0.15gSB·kgFFM−1 (p=0.001; W=0.178); and higher total gastrointestinal upset compared to CTRL, PLA and 0.15gSB·kgFFM−1 (p<0.001; W=0.323). ConclusionsThere were dose- and gender-related differences in extracellular buffering capacity and ergogenic potential of sodium bicarbonate. The study suggested a detrimental impact of gastrointestinal upset on performance.