If you’ve come across breathing performance or CO₂ tolerance work, you’ve likely encountered the term BOLT score. This article explains exactly what it is, how to measure it accurately, what the results mean, and how to use the data in a professional football context.
What Is the BOLT Score?
BOLT stands for Body Oxygen Level Test. Despite the name, it is not a direct measure of oxygen — it is a practical, non-invasive assessment of CO₂ tolerance: how long the body can comfortably sustain a breath hold before triggering the urge to inhale.
The test was developed and popularised by Patrick McKeown of the Buteyko Institute and is used in clinical respiratory rehabilitation as well as elite sport performance settings.
It measures the functional threshold at which the body’s chemoreceptors — primarily the carotid bodies — detect rising CO₂ and send the urge-to-breathe signal to the respiratory control centres in the brainstem.
Why CO₂ Tolerance Matters in Football
CO₂ is not simply a metabolic waste product. Through the Bohr Effect, CO₂ is the primary regulator of oxygen release from haemoglobin into working muscle tissue.
Athletes with low BOLT scores (poor CO₂ tolerance):
- Breathe at higher minute volumes during exercise
- Exhale CO₂ before it can facilitate tissue oxygen delivery
- Experience earlier muscle acidification and fatigue
- Recover slower between high-intensity efforts
- Show greater cognitive degradation under physical stress
Athletes with high BOLT scores:
- Breathe more efficiently — more work per breath
- Sustain higher intensities before respiratory fatigue onset
- Recover faster between sprint efforts
- Maintain decision quality later in matches
How to Administer the BOLT Test
Preparation: The test should be administered after at least 10 minutes of seated rest. The athlete should not have exercised in the previous 2 hours. Avoid caffeine for 2 hours prior.
Procedure:
- Athlete sits comfortably, spine upright, hands on thighs
- Take a normal breath in through the nose
- Let a normal breath out through the nose (not a forced exhale — a relaxed, natural exhale)
- Pinch the nose gently with thumb and forefinger
- Start the timer
- Hold until the first involuntary urge to breathe — not until maximum discomfort
- Stop the timer and note the time in seconds
Critical point: The BOLT score is the time to the first urge, not the maximum hold. Encourage athletes not to “push through” the first signal — this invalidates the measurement. The first contraction or urge is the data point.
Frequency: Measure at baseline, then every two weeks during an active programme. Measure at the same time of day and under the same conditions for consistency.
Interpreting the Results
Based on data from our programme with professional football squads:
| BOLT Score | Interpretation | Typical Profile |
|---|---|---|
| Under 10s | Severely dysfunctional | Chronic stress, poor sleep, likely mouth breather |
| 10–15s | Dysfunctional | Upper-chest breather, mouth breathing common |
| 15–20s | Below average | Functional but inefficient |
| 20–25s | Average | Baseline acceptable; improvement available |
| 25–35s | Good | Efficient nasal breather, good CO₂ tolerance |
| 35–40s | Very good | Strong baseline; likely some prior training |
| 40s+ | Elite | Trained endurance athlete or advanced practitioner |
In our assessment of professional Ekstraklasa footballers, the average baseline BOLT score was 16 seconds. This aligns with recreational athletes — confirming that high training volume does not self-correct breathing mechanics.
Using BOLT Data in a Performance Context
Individual Profiling: BOLT scores reveal which athletes are carrying a hidden respiratory deficit. A player with a BOLT of 12 seconds is running every training session with a physiological handbrake on — regardless of their GPS data.
Squad Variance: High variance in BOLT scores within a squad (e.g., range of 10–28 seconds) suggests significant inequality in physiological readiness. Players at the low end will reach exhaustion faster, recover slower, and require longer between high-intensity efforts.
Programme Response Monitoring: BOLT scores respond relatively quickly to targeted breathing training — typical improvements of 5–12 seconds in the first 8 weeks. This makes the BOLT an excellent short-cycle outcome measure, unlike VO₂max which requires months of training stimulus to move meaningfully.
Readiness Integration: When combined with WHOOP or Oura HRV data, BOLT score trajectories provide a composite view of nervous system readiness. Athletes showing simultaneous HRV suppression and BOLT regression may be experiencing cumulative load — useful data for managing training peaks.
Common Mistakes When Administering the BOLT Test
1. Athlete holds past the first urge This is the most common error. Athletes (especially competitive ones) resist the urge and push for a higher number. Remind them: the first involuntary contraction or urge is the score. Willpower is not being measured.
2. Forced exhale before the hold Some athletes exhale fully before pinching the nose, creating a different physiological starting condition. The test requires a normal, relaxed exhale — approximately 60–70% of tidal volume, as in normal breathing.
3. Administering after exercise Testing after a training session will yield artificially lower scores due to elevated metabolic CO₂ and respiratory drive. Always test at rest.
4. Inconsistent testing conditions Environmental temperature, stress level, and hydration all affect BOLT scores marginally. Consistency in testing conditions matters more than absolute precision.
What to Do With a Low Score
A BOLT score below 20 seconds indicates that structured breathing training will produce measurable physiological returns.
The AirFlow Performance programme targets a minimum of 25 seconds within 12 weeks — a threshold at which the most significant performance gains (reduced red-zone time, improved sprint recovery, more consistent high-intensity output) become measurable in GPS and WHOOP data.
If you’d like to run baseline BOLT assessments for your squad and discuss what a structured programme might look like, book a discovery call →.
The BOLT test is a practical screening tool, not a clinical diagnostic. For athletes with known respiratory conditions, consult relevant medical staff before initiating breathing performance training.