**Background:** High-intensity functional training (HIFT), including CrossFit, stresses both aerobic and anaerobic energy pathways. Sodium bicarbonate (SB) is a well-established ergogenic aid for high-intensity exercise lasting 30 s to 12 min, acting by increasing extracellular buffering capacity. However, only two prior studies examined SB in CrossFit-specific protocols, and data linking bicarbonate kinetics, gastrointestinal (GI) side effects, and anaerobic performance after high-dose SB with carbohydrate co-ingestion are lacking. The authors hypothesized that 0.4 g·kg⁻¹ BM SB + 15 g CHO ingested 90 min before repeated Wingate bouts would elevate blood HCO₃⁻ above the ergogenic threshold (>6 mmol·L⁻¹) and minimize performance decrements while reducing GI distress.
**Methods:** Twenty CrossFit-trained participants (9 male, 10 female after one dropout; age 37 ± 8 years; body mass 75.1 ± 13.1 kg) completed this randomized, double-blind, placebo-controlled crossover trial. The protocol comprised four visits: familiarization (T1), control (CTRL, no supplement, T2), and two experimental visits (T3, T4) where participants ingested SB+CHO or PLA+CHO in random order, separated by 7-day washout. Capillary blood was collected at 12 time points: baseline (−90′ EX), 30, 60, 75, and 90 min post-ingestion (0′ EX), immediately after each of six 15-s WAnT bouts (WAnT_1 to WAnT_6 POST), and 45 min recovery (+45′ EX). A standardized 10-min warm-up occurred between 77–87 min post-ingestion. Performance indices (peak power [PP], average power [AP], minimum power [MP], power drop [PD], time to peak power [TtoPP]) were recorded. GI symptoms were assessed 120 min post-ingestion using a 19-item NRS questionnaire (0–10 scale). Statistical analyses used RM ANOVA with Bonferroni post-hoc, Friedman's ANOVA for GI data, and Spearman correlations.
**Key Results:** Blood HCO₃⁻ peaked at 33.0 ± 2.5 mmol·L⁻¹ at 75 min post-ingestion (−15′ EX) in SB+CHO, with 79% of participants peaking at this time point. Mean increase from baseline was +7.8 ± 1.9 mmol·L⁻¹; 84% of participants achieved increases >6 mmol·L⁻¹ (almost certain ergogenic threshold) and 16% achieved 4–6 mmol·L⁻¹. At 0′ EX (90 min post-ingestion, after warm-up), mean increase was +6.1 ± 1.9 mmol·L⁻¹ (52.6% >6 mmol·L⁻¹, 47.4% 4–6 mmol·L⁻¹). Blood pH was significantly higher in SB+CHO vs PLA+CHO and CTRL at all post-ingestion time points. Lactate was higher after SB+CHO vs comparators at most post-exercise time points. Performance declined across consecutive WAnT bouts in all conditions. Mean PP across 6 bouts was significantly higher in SB+CHO (8.09 ± 1.00 W·kg⁻¹) and PLA+CHO (8.31 ± 1.05 W·kg⁻¹) vs CTRL (7.65 ± 1.02 W·kg⁻¹; p=0.000, η²p=0.638), but the main effect lost significance when gender was included in the model. There was no significant difference between SB+CHO and PLA+CHO for any performance index. No significant linear relationships were found between HCO₃⁻ increase and WAnT performance. GI symptoms were substantially higher in SB+CHO vs CTRL and PLA+CHO for stomach problems (median 2.0 vs 0.0 vs 0.0; p=0.000, Kendall's W=0.445), flatulence (p=0.007), urge to defecate (p=0.000), belching (p=0.001), diarrhea (p=0.000), and total GI symptoms (median 26.0 vs 4.0 vs 11.0; p=0.000, W=0.387). Severe GI symptoms did not differ between conditions (p=0.819). Regression analysis revealed significant inverse correlations between total GI symptoms and mean PP (r=−0.495, p=0.031), AP (r=−0.674, p=0.002), and MP (r=−0.585, p=0.008) in SB+CHO.
**Clinical Implications:** This study demonstrates that acute ingestion of 0.4 g·kg⁻¹ BM SB+CHO effectively elevates blood bicarbonate above the ergogenic threshold in most CrossFit-trained athletes, with peak HCO₃⁻ occurring approximately 75 min post-ingestion. However, the ergogenic benefit was negated by significant GI distress, which inversely correlated with power output. The co-ingestion of 15 g CHO did not prevent GI symptoms. The warm-up caused a non-significant reduction in HCO₃⁻ (−1.6 ± 1.7 mmol·L⁻¹), which may impact buffering capacity at exercise onset. These findings suggest that for high, acute SB doses, individualization of ingestion timing is critical to align peak bicarbonate with exercise while minimizing GI upset. Future research should monitor GI symptoms at multiple time points and consider longer intervals between ingestion and exercise, or split-dose/chronic protocols, to separate peak bicarbonate from peak GI distress.