Post-Workout Bicarbonate (NaHCO3) Buffers Performance Decline on 2nd Bout of Exhaustive Exercise by 62%!

AM/PM cyclists rejoice: Bicarbonate is going to get you back into the saddle.

It sounds only logical that the provision of 0.3g/kg of sodium bicarbonate after a bout of cycling to full exhaustion would increase the blood pH of nine healthy, active males significantly. That it would also boost their performance on a second incremental exercise test, though, was not necessarily to be expected - irrespective of the evidence that pre-exercise ingestion of the same amount of NaHCO3 was consistently found to increase athletic performance during high-intensity exercise of short duration (1-10 min | Carr 2011).

Exactly that, however, is what scientists from the "Department of Sport and Physical Activity" at the Edge Hill University and the "Department of Life Sciences" at the University of Derby (Gough 2017).
The study evaluated the effects of the ingestion of the formerly mentioned whopping dose of 0.3g/kg sodium bicarbonate (NaHCO3) on post-exercise acid-base balance recovery kinetics and subsequent high-intensity cycling time to exhaustion.

In a counterbalanced, crossover design, nine healthy and active males (age: 23±2 years, height: 179±5 cm, body mass: 74±9 kg, peak mean minute power (WPEAK) 256±45 W, peak oxygen uptake (VO2PEAK) 46±8 ml/kg/min) performed a graded incremental exercise test, two familiarisation and two experimental trials.

Figure 1: Schematic illustrating protocol for experimental trials. Key: HR = heart rate, blood = [BLa-], pH, [HCO3-], [K+], [Na+], [Ca++] and [Cl-], V̇ O2 = oxygen uptake, V̇ E = minute ventilation, RER = respiratory exchange ratio, RPD = ratings of perceived dyspnea, RPEL = ratings of perceived exertion localized to the legs, AD = abdominal discomfort, GF = gut fullness, BUR = bowel urgency rating, R=recovery. ** Treatment ingestion (30-35 mins recovery | from Gough 2017).

As you can read in the abstract and full text of the study, the experimental trials consisted of cycling to volitional exhaustion (TLIM1) at 100% WPEAK on two occasions (TLIM1 and TLIM2) interspersed by a 90 min passive recovery period. About the supplementation protocol, the authors write the following:

"Using a double blind approach, 30 min into a 90 min recovery period participants ingested either 0.3 g.kg-1 body mass sodium bicarbonate (NaHCO3) or a placebo (PLA) containing 0.1 g/kg body mass sodium chloride (NaCl) mixed with 4 ml/kg tap water and 1 ml/kg orange squash 30 to 35 min into a 90 min passive recovery period. Treatments were administered double blind, with trials counterbalanced. " (Gough 2017). 

When they analyzed the data from the first and second cycling session, the scientists found that the mean differences between TLIM2 and TLIM1 were larger for PLA compared to NaHCO3 (-53±53 vs. -20±48 s; P=0.008, d=0.7, CI=-0.3, 1.6).

Figure 2: Changes in time to volitional exhaustion for indiv. participants on placebo (PLA) and NaHCO3 treatments.* PLA > NaHCO3 (P <0.01) | the orange and red marks have been added to the figure from Gough et al. 2017

Just as in previous trials, however, the advantage showed a significant inter-personal difference, the correlation of which with the significant changes in blood lactate and pH levels the scientists either didn't calculate or simply didn't report. Accordingly, Gough et al. can't tell us more than that "[i]t is likely both the acceleration of recovery, and the marked increases of acid-base after TLIM1 contributed to greater TLIM2 performance compared to the PLA condition" - what they cannot tell us, however, is why some subjects (see red marks) simply didn't benefit while others actually outperformed their previously fully recovered selves on the 2nd trial.

Was it gastrointestinal distress? I can't tell because correlation data isn't available for that either. What I can tell you, though, is that there was a main effect for time observed for abdominal discomfort (AD) following NaHCO3 (P=0.008), whereby AD was greater at 60 (z=2.032, P=0.042) and 90 min (z=2.232, P=0.026) compared to 30 min recovery. No differences in AD were observed between NaHCO3 and PLA at 30 (median NaHCO3=0 vs. PLA=0; z=-0.333, P=0.739), 60 (0 vs. 1; z=0.318, P=0.750) or 90 min (0 vs. 2; z=1.186, P=0.236) of recovery between treatments. Gut fullness wasn't affected by either treatment, but some subjects obviously thought that a bowel movement was approaching 60 or 90 minutes into the recovery on bicarb.
References:

• Carr, Amelia J., Will G. Hopkins, and Christopher J. Gore. "Effects of acute alkalosis and acidosis on performance." Sports medicine 41.10 (2011): 801-814.
• Gough, Lewis A., et al. "Ingestion of Sodium Bicarbonate (NaHCO3) Following a Fatiguing Bout of Exercise Accelerates Post-Exercise Acid-Base Balance Recovery and Improves Subsequent High-Intensity Cycling Time to Exhaustion." International Journal of Sport Nutrition and Exercise Metabolism (2017): 1-25.