You'd expect stacking two buffers to beat taking one. In a new study of highly trained female CrossFit athletes, it didn't. Sodium bicarbonate finished first, and the combination of bicarbonate and sodium citrate finished well behind it.
The study, published in the International Journal of Sports Physiology and Performance (2025), compared three buffering strategies against a placebo. Only one of them clearly worked.
What Buffers Actually Do
Hard efforts lasting roughly one to ten minutes produce a lot of hydrogen ions in the muscle and blood. Those ions drive down pH, and that acidity is closely tied to the burning, heavy-legged slowdown late in a hard effort.
Sodium bicarbonate and sodium citrate are "extracellular buffers." They raise the blood's capacity to soak up acid, which may help muscle push hydrogen ions out of the working cells. In theory, a higher blood bicarbonate concentration before exercise means a better chance of holding pace when it hurts.
Bicarbonate is the better-studied option, but it is notorious for causing stomach trouble. Citrate is often pitched as the gentler alternative, and some athletes combine the two hoping for the best of both. This study tested that logic directly.
The Study: Four Conditions, Ten Athletes
Researchers at Edge Hill University and Beijing Sport University recruited ten highly trained female CrossFit athletes. Each completed four 6-km cycling time trials in a randomized, crossover, placebo-controlled design. Before each trial, they took one of the following in enteric-coated capsules:
- Sodium bicarbonate (SB) at 0.3 g/kg body mass
- Sodium citrate (SC) at 0.3 g/kg
- Both combined (SBC), matched to the same total dose
- Placebo (PLA)
The athletes used a time-to-peak ingestion strategy. Instead of everyone dosing at the same fixed time, timing was individualized around when each athlete's blood buffering peaked. Blood acid-base balance was measured before ingestion, before exercise, and after exercise.
The Results: Bicarbonate Wins Clearly
Before exercise, blood bicarbonate was significantly higher with SB than with both placebo (+6.5 mmol/L) and sodium citrate (+2.3 mmol/L). That gap carried over to the time trial.
The 6-km time trial finishing times for bicarbonate were:
- 21.5 seconds faster than placebo
- 11.6 seconds faster than sodium citrate
- 17.2 seconds faster than the combination
Blood lactate was also higher after the bicarbonate trial than after placebo (about 2.4 mmol/L higher). That isn't a downside. A buffered athlete can often tolerate more glycolytic work, which tends to show up as more lactate in the blood.
The Surprise: Stacking Didn't Help
Neither sodium citrate nor the bicarbonate-plus-citrate combo performed significantly better than placebo. The differences were small and not statistically meaningful (about 9.9 s for SC and 4.3 s for SBC versus placebo).
The stack may feel like insurance, but this result suggests it isn't. When the total dose was held constant, the combination effectively gave athletes less bicarbonate, and the bicarbonate seems to have been the active ingredient. Citrate didn't make up the difference.
The study's design can't prove exactly why the combo underperformed, so treat any mechanism as a hypothesis. A plausible reading is that a half-dose of bicarbonate wasn't enough to raise blood buffering sufficiently, and citrate on its own didn't raise it enough either. The practical message is that more products doesn't mean more benefit.
The Catch: GI Symptoms
Bicarbonate didn't come free. Before exercise, GI symptom scores were higher with SB than with placebo (about 2.4 arbitrary units higher) and with sodium citrate (about 2.2 higher).
That is the usual trade-off with bicarbonate. Even with enteric-coated capsules and individualized timing, it caused more stomach discomfort than the other options. Whether that discomfort is worth about 20 seconds over 6 km is a personal call, and it depends on how your gut reacts.
Practical Takeaways
If you're considering trying this, here is how the study's approach translates to practice:
- Dose: 0.3 g/kg body mass of sodium bicarbonate, the dose used in the study. A 65 kg athlete would take about 19.5 g.
- Form: Enteric-coated capsules, which are designed to reduce stomach upset by releasing the bicarbonate further along the gut.
- Timing: Individualize it. Ingestion timing in bicarbonate research typically falls somewhere around 60 to 180 minutes before exercise, because each person's blood bicarbonate peaks at a different time. Test your own peak in practice if you can.
- Food: Take it with a carbohydrate-containing meal, which many athletes find eases GI side effects.
- Who it's for: Efforts of roughly 1 to 10 minutes, including CrossFit workouts, rowing, and 400 to 1,500 m running or similar events.
- Trial first: Never debut a buffer on competition day. Rehearse the dose, timing, and meal in training so you know how your stomach responds.
- Skip the stack: Based on this study, adding citrate isn't worth the complexity.
Limitations
This was a small study of ten women. That is a respectable sample for a tightly controlled crossover trial of highly trained athletes, but it limits how confidently the findings extend to other people. The test was also a 6-km cycling time trial rather than an actual CrossFit workout, so the results may not transfer perfectly to mixed-modality events. A published erratum also exists for the paper, so anyone citing exact figures should check the journal's current version. Larger studies with sport-specific tests would help confirm the result.
Bottom Line
In this group of trained female CrossFit athletes, sodium bicarbonate at 0.3 g/kg in enteric-coated capsules improved blood buffering and cut 6-km time trial time by 21.5 seconds against placebo. Sodium citrate and the combination didn't clearly beat placebo. The price was more GI discomfort, so rehearse the plan in training before relying on it in competition.
