Internal Study: The pHastr Effect on FTP Performance

Subject: Emily · Test: FTP (Functional Threshold Power) · Comparison: With pHastr vs No pHastr · Date: March 19, 2026

pHastr is a sodium bicarbonate (NaHCO₃) supplement designed to extend the body's extracellular buffering capacity during high-intensity exercise. During intense efforts, working muscles accumulate hydrogen ions (H⁺), causing metabolic acidosis — the physiological "burn" that limits output. Bicarbonate increases the blood's ability to neutralize H⁺, allowing the athlete to sustain higher intensities for longer. This is what that looked like in Emily's lab data.

1. Physiological Rationale

1.1 The Acid-Base Problem at High Intensity

During an FTP test, the body leans hard on anaerobic glycolysis to regenerate ATP. The byproducts are lactate and hydrogen ions. As H⁺ accumulates inside the muscle cell, intracellular pH drops — metabolic acidosis. That acidic environment:

  • Inhibits key glycolytic enzymes (e.g., phosphofructokinase)
  • Impairs calcium release and contractile function
  • Reduces the rate of ATP regeneration
  • Accelerates the onset of fatigue

1.2 How Sodium Bicarbonate Works

Ingesting NaHCO₃ raises blood bicarbonate concentration ([HCO₃⁻]), creating a stronger electrochemical gradient that pulls H⁺ out of working muscle cells and into the bloodstream. Once in the blood, H⁺ is neutralized by bicarbonate:

H⁺ + HCO₃⁻ → H₂O + CO₂

The resulting CO₂ is transported to the lungs and exhaled. The net result:

  • Delays the drop in intramuscular pH
  • Preserves glycolytic enzyme activity and ATP production
  • Maintains muscle excitability and contractile force
  • Lets the athlete sustain higher power before fatigue limits output

Bicarbonate does not eliminate fatigue. It delays it by extending the window before acidosis becomes performance-limiting. That's why the effect is most pronounced during high-intensity efforts lasting 30 seconds to 12 minutes — exactly the duration profile of an FTP test.

1.3 Additional Mechanisms

  • Ion redistribution. NaHCO₃ alters the distribution of Na⁺, K⁺, Ca²⁺, and Cl⁻ across cell membranes, helping preserve muscle excitability.
  • Monocarboxylate transporter (MCT) activity. The improved H⁺ gradient enhances lactate efflux from muscle via MCT transporters, further reducing intracellular acidosis.
  • Glycolytic flux. Some evidence suggests NaHCO₃ may alter glycolytic intermediate concentrations, though this is intensity-dependent.
  • Reduced oxidative stress. Post-exercise, bicarbonate may attenuate reactive oxygen species (ROS) production, potentially aiding recovery.

2. Observed Differences in Emily's FTP Test

Data processed with 30-second centered rolling average and IQR-based outlier handling (factor 2.5). Summary statistics computed on outlier-handled raw series.

2.1 Mean Values Across Full Test

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2.2 Peak Values (99th Percentile)

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3. Metric-by-Metric Interpretation

3.1 VO₂ & VCO₂ — Higher Metabolic Output

Mean VO₂ was +7.7% higher and VCO₂ was +11.8% higher with pHastr. At peak (p99), VO₂ was +14.9% and VCO₂ was +19.0% higher. The buffering reaction (H⁺ + HCO₃⁻ → H₂O + CO₂) generates additional CO₂ beyond what aerobic metabolism alone produces — this "non-metabolic" CO₂ must be exhaled, inflating VCO₂. At the same time, reduced acidosis allowed Emily to sustain higher power outputs, driving true aerobic demand (VO₂) upward. The larger gain in VCO₂ vs VO₂ is a classic signature of bicarbonate supplementation.

3.2 RER — Shift in Substrate Utilization Signal

Mean RER rose from 0.928 to 0.953 (+2.7%); peak RER from 1.205 to 1.269 (+5.3%). RER = VCO₂ / VO₂. Because bicarbonate artificially elevates VCO₂ through the buffering chemistry, RER is inflated beyond what substrate oxidation alone would predict. A higher RER does indicate a greater carbohydrate contribution (consistent with higher intensity), but part of the elevation is a direct chemical artifact of buffering. Caution is warranted when reading RER as a pure substrate marker in bicarbonate trials.

3.3 Heart Rate — Higher Cardiovascular Load

Mean HR was +10.9 bpm higher with pHastr (134 vs 145 bpm). Peak HR was only marginally higher (185 vs 188 bpm). Reduced acidic inhibition allowed Emily to push into higher absolute intensity zones that would otherwise have been unsustainable. A higher mean HR across the entire test confirms she worked at a greater cardiovascular load throughout — not just at the end. The near-identical peak HR suggests she reached a similar maximal ceiling but spent more time at higher intensities with pHastr.

3.4 Ventilation & Tidal Volume — Modest Changes

Ventilation was only +2.7% higher; tidal volume +1.7% higher; respiratory rate +2.1% higher. The dominant differences between conditions were metabolic and cardiovascular, not ventilatory. The body did increase breathing to expel the additional CO₂ from buffering, but the changes were modest — suggesting that breathing mechanics were not a limiting factor in either condition, and that the pHastr effect operated primarily at the muscle and cardiovascular level.

3.5 Calorie Burn Rate — Higher Energy Expenditure

Mean calorie burn rate was +8.6% higher; peak was +15.8% higher with pHastr. Higher VO₂ and VCO₂ translate directly to higher estimated energy expenditure. Emily was burning more calories per unit time because she was working at a higher absolute intensity throughout the test — consistent with the overall picture of pHastr enabling a higher sustained workload.

4. Summary — The "pHastr Effect" in Emily's Data

  • Aerobic metabolism. VO₂ +7.7% mean, +14.9% peak. Reduced acidosis allowed higher sustained aerobic power output.
  • CO₂ production. VCO₂ +11.8% mean, +19.0% peak. Extra CO₂ from the H⁺ + HCO₃⁻ buffering reaction, plus higher aerobic demand.
  • Substrate signal. RER +2.7% mean, +5.3% peak. Inflated by buffering chemistry; also reflects higher carbohydrate use at greater intensity.
  • Cardiovascular load. HR +8.1% mean (+10.9 bpm). Higher absolute intensity sustained throughout the test.
  • Ventilatory mechanics. Ventilation +2.7%, tidal volume +1.7%. Modest increase to expel extra CO₂; not a limiting factor.
  • Energy expenditure. Calorie burn +8.6% mean, +15.8% peak. Direct consequence of higher VO₂ and VCO₂.

Bottom line: pHastr did not simply make the FTP test feel easier — it enabled Emily to work at a measurably higher physiological intensity throughout the test. The data shows a clear and consistent "pHastr Effect" across all major metabolic and cardiovascular markers, with the largest gains appearing at near-peak intensities (p99), exactly where bicarbonate buffering is most effective.

5. Notes & Considerations

  • RER interpretation. Values above 1.0 during bicarbonate trials should not be read as pure substrate data — the buffering chemistry inflates VCO₂ independently of fat/carbohydrate oxidation.
  • Individual response. Bicarbonate response varies between individuals. Emily's data shows a clear positive response, but this is not universal.
  • Dosing & timing. The ISSN recommends 0.3 g/kg body mass taken 60–180 minutes before exercise for optimal blood alkalosis at the start of effort.
  • GI side effects. Some athletes experience bloating, nausea, or GI discomfort. Taking bicarbonate with a carbohydrate meal or in enteric-coated capsules can substantially reduce this risk.
  • Test order. Without randomization and washout confirmation, order effects (e.g., fatigue, learning) cannot be fully excluded from this comparison.

References: Siegler et al. (2016) Sports Medicine Open; Hadzic et al. (2019) J Sports Sci Med; Grgic et al. (2021) ISSN Position Stand, J Int Soc Sports Nutr; Gurton et al. (2024) Eur J Appl Physiol. Data: Emily_No_pHastr.csv & Emily_with_pHastr.csv.