BOLT Test (Body Oxygen Level Test)
A simple breath-hold assessment developed by Patrick McKeown to measure CO2 tolerance and breathing efficiency, used to track progress in breathing training
Bottom Line
The BOLT (Body Oxygen Level Test) is a simple, free assessment that measures how efficiently your body uses oxygen. Developed by Patrick McKeown of Oxygen Advantage, it's become a standard tool in breathwork communities.
What it measures:
- CO2 tolerance (not oxygen levels despite the name)
- Breathing pattern efficiency
- Chemoreceptor sensitivity
- Overall respiratory health
Why it matters:
- Low scores correlate with dysfunctional breathing patterns
- Scores can double or triple with 1-2 weeks of practice
- Provides objective feedback for breathing training
- Links to conditions like sleep apnea, anxiety, ADHD
James Nestor (author of "Breath") discussed with Tim Ferriss how many health conditions trace back to breathing dysfunction, and the BOLT test is a quick way to assess this.
A free, 1-minute test everyone should try. Low scores suggest room for improvement through nasal breathing and breath training. Use it to track progress with any breathwork practice.
Science
What BOLT Actually Measures:
Despite "oxygen" in the name, BOLT measures your tolerance to rising CO2 levels, specifically, how long until your body's chemoreceptors trigger the urge to breathe.
The Physiology:
Carbon Dioxide Tolerance:
- CO2 is the primary driver of breathing urge
- Higher tolerance = more efficient breathing
- Lower tolerance = over-breathing, inefficiency
- Chemoreceptors in brain stem detect CO2 levels
Why CO2 Tolerance Matters:
- Over-breathers have low CO2 tolerance
- This leads to chronic hyperventilation
- Results in reduced oxygen delivery to tissues (Bohr effect)
- Creates cycle of inefficient breathing
The Bohr Effect:
- Hemoglobin releases oxygen more readily in presence of CO2
- Low CO2 = oxygen stays bound to hemoglobin
- Paradox: over-breathing reduces oxygen delivery
BOLT Correlations:
Low BOLT (<20 seconds):
- Chronic mouth breathing
- Sleep-disordered breathing
- Exercise intolerance
- Anxiety and panic symptoms
- Asthma symptom severity
High BOLT (>40 seconds):
- Efficient breathing patterns
- Better exercise capacity
- Improved stress resilience
- Better sleep quality
Research:
- Studies show BOLT correlates with asthma control
- Improvement in BOLT parallels reduction in symptoms
- Used as outcome measure in breathing intervention studies
Supporting Studies
1 peer-reviewed study
View all studies & compare research →Practical Protocol
How to Perform the BOLT Test:
Preparation:
- Sit in relaxed position
- Rest for several minutes
- Breathe normally through nose
The Test:
1. Take a normal breath IN through nose 2. Take a normal breath OUT through nose 3. Pinch your nose to hold breath 4. Start timer 5. Hold until FIRST DISTINCT urge to breathe 6. Stop timer at first: - Involuntary swallow - Diaphragm contraction - Desire to breathe 7. Resume normal breathing (shouldn't need to gasp)
Critical Points:
- Do NOT hold until desperate
- Stop at FIRST urge, not maximum hold
- If you gasp afterward, you held too long
- Should be able to resume normal breathing immediately
Scoring:
| BOLT Score | Rating | Implication |
|---|---|---|
| <10 sec | Poor | Significant breathing dysfunction |
| 10-20 sec | Below average | Room for improvement |
| 20-30 sec | Average | Typical for most adults |
| 30-40 sec | Good | Healthy breathing pattern |
| 40+ sec | Excellent | Optimal breathing efficiency |
When to Test:
- Morning upon waking (most accurate)
- Before meals
- When calm and relaxed
- Same time daily for consistency
Improving Your Score:
| Practice | Effect |
|---|---|
| Nasal breathing 24/7 | Foundation for improvement |
| Mouth taping at night | Prevents nocturnal mouth breathing |
| Breath holds after exhale | Builds CO2 tolerance |
| Reduced breathing exercises | Normalizes breathing volume |
| Light physical exercise with nasal breathing | Functional adaptation |
Risks & Side Effects
The Test Itself:
- Virtually no risk when done correctly
- Don't hold to maximum (that's not the test)
- Stop at first urge to breathe
- Resume normal breathing immediately
Breath Training (to improve BOLT):
- Don't overdo breath holds
- Never do breath holds in water
- Stop if dizzy or uncomfortable
- Progress gradually
Who Should Be Cautious:
- Panic disorder (may trigger anxiety initially)
- Severe asthma (consult doctor)
- Cardiovascular conditions
- Pregnancy
- Recent surgery
Warning Signs:
- Dizziness or lightheadedness
- Headache
- Numbness or tingling
- Anxiety or panic
- These suggest stopping and resting
Contraindications for Intensive Breath Training:
- Epilepsy
- Severe cardiovascular disease
- Uncontrolled hypertension
- Recent stroke
Risk Level: Very low for the test itself
Who It's For
Everyone Should Test:
- Free, takes 1 minute
- Provides baseline for breathing health
- No equipment needed
Especially Valuable For:
- Those with chronic mouth breathing
- People with anxiety or panic
- Sleep apnea or snoring
- Asthma sufferers
- Athletes seeking performance gains
- Anyone doing breathwork training
- Those with exercise intolerance
Use Cases:
- Baseline assessment before breath training
- Track progress with nasal breathing practice
- Monitor respiratory health over time
- Correlate with other health markers
How to Track Results
Daily BOLT Tracking:
- Test each morning upon waking
- Same conditions each time
- Record in journal or app
- Note relevant factors (sleep quality, stress)
What to Track:
- BOLT score (seconds)
- Time of day
- Conditions (rested, stressed, etc.)
- Any breathing practices done
Progress Expectations:
| Timeframe | Typical Improvement |
|---|---|
| Week 1 | 5-10 second increase possible |
| Week 2-4 | Scores can double |
| Month 2-3 | Continued gains with practice |
| Long-term | Maintenance of improved scores |
Factors Affecting Score:
- Sleep quality (poor sleep = lower score)
- Stress levels
- Recent exercise
- Illness or congestion
- Caffeine or alcohol
Correlate With:
- Sleep quality
- Energy levels
- Anxiety/stress levels
- Exercise performance
- HRV if tracking
Top Products
Resources:
Books:
- The Oxygen Advantage by Patrick McKeown - Original source
- Breath by James Nestor - Broader breathing science
Apps:
- Oxygen Advantage app - Official, includes BOLT tracking
- Breathwrk - General breathing exercises
- Various timer apps - Simple tracking
For Improvement:
- Mouth tape - See mouth taping intervention
- Nasal breathing - Foundation practice
- CO2 tolerance training - Direct training
Training:
- Oxygen Advantage instructor directory
- Buteyko breathing practitioners
- Breathwork coaches
Cost Breakdown
The Test: FREE
- No equipment needed
- Just a timer (phone works)
- Can do anywhere
Optional Tracking:
- Notebook: $0
- App (many free options): $0
- Spreadsheet: $0
Breath Training Tools (optional):
| Tool | Purpose | Cost |
|---|---|---|
| Mouth tape | Night nasal breathing | $5-15 |
| Breathing app | Guided exercises | Free-$10/mo |
| Oxygen Advantage book | Full program | $15-20 |
| Capnometer | Advanced CO2 tracking | $200+ |
Courses (optional):
- Oxygen Advantage certification: $200-500
- Various breathwork courses: $50-500
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Discussed in Podcasts
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Patrick McKeown explains the BOLT test and CO2 tolerance
McKeown introduces the Body Oxygen Level Test and explains how it measures breathing efficiency through CO2 tolerance assessment.
"In 1998, he found an article in an Irish newspaper about the Bidayeiko breath method. He tried the exercise to unlock his nose and was struck by how well it actually worked by using the nose."
17% of people are persistent mouth breathers
McKeown reveals that research shows 17% of individuals are persistent mouth breathers, which deteriorates health and breathing efficiency.
"Breathing is so boring that researchers haven't actually sat down. Both studies come in that individuals were persistent mouth breeders at 17%."
BOLT test as the first assessment for hiking fitness
Chase Tucker explains that the BOLT test is his first-line assessment for hiking readiness, measuring CO2 tolerance which has been used since 1979.
"First thing he would do is a bolt test, body oxygen level test to see if he can tolerate a high level of carbon dioxide in his bloodstream. Real simple."
Hybrid athlete approach for hiking performance
Tucker advocates for a hybrid athlete approach to hiking fitness, combining strength training with trail running to build both muscular endurance and aerobic capacity.
"It's certainly nice to develop a base of strength and to throw some weights around in the gym and that will help you in hiking in many, many different ways. But also the running aspect will really help you build your zone too, build your aerobic base."
McKeown explains the BOLT test and ideal scores
Patrick McKeown walks through the BOLT test procedure and explains that a good score is 40 seconds, while most athletes only manage 10-20 seconds.
"We have the BOLT about, you know, it stands for the body oxygen level test. And it's a measurement of comfortable breath hold time. So the individual takes a small breath in, a small breath out, and they pinch their nose to hold their breath."
Athletes with low BOLT scores have huge room for improvement
McKeown references William McArdle's research showing athletes should be able to hold their breath for 40 seconds on exhalation, but most only manage 10-20.
"On page 289 of that book, he says that when an athlete exhales, they should be able to hold their breath for up to 40 seconds before the urge is there to initiate respiration."
How breathing volume affects health and performance
McKeown draws an analogy between breathing volume and food/water intake, arguing we should breathe just the right amount, not too much.
"There's a certain amount of food that we should be eating each day. There's a certain amount of water we should be drinking each day. And there's a certain amount of air we should be breathing each day. How much air should we breathe? It shouldn't be too much. It shouldn't be too little. It should be just right."
How the BOLT test measures CO2 tolerance
Brad explains the BOLT test procedure step by step, emphasizing that it measures how much carbon dioxide can accumulate before the urge to breathe.
"Body Oxygen Level Test measures how much carbon dioxide can accumulate until you feel the urge to take a breath. So here's what you do. You breathe normally through your nose for a few cycles. Don't take a bigger breath than normal."
Brad's personal BOLT score improvement journey
Brad shares how he improved from a sub-20-second BOLT score to consistently hitting 35 seconds in just a few weeks of nasal breathing practice.
"I was under 20 seconds, a pathetic under 20 seconds for my first few bolt tests. And in just a few weeks of practice, I was at a minimum of 20 seconds."
Who to Follow
Developers:
- Patrick McKeown - Created BOLT, Oxygen Advantage founder
- Based on Buteyko breathing method principles
Advocates:
- James Nestor - Author of "Breath," discusses on Tim Ferriss Show
- Brian Mackenzie - Uses in Shift Adapt performance programs
- Dr. Andrew Huberman - Discusses CO2 tolerance importance
Research Context:
- Konstantin Buteyko (1923-2003) - Original researcher on CO2 tolerance
- Patrick McKeown modernized and popularized the test
Synergies & Conflicts
Breathing Stack:
- Nasal Breathing - Foundation practice
- Mouth Taping - Night training
- CO2 Tolerance Training - Direct improvement
- Cyclic Sighing - Stress management
Use BOLT to Track:
- Progress with any breathwork protocol
- Impact of lifestyle changes on breathing
- Recovery from illness
- Effects of altitude training
Correlate With:
- HRV measurements
- Sleep quality scores
- Exercise performance
- Anxiety/stress levels
Best Practices:
- Test BOLT before starting new breathwork
- Retest weekly during training
- Use consistent conditions
- Track alongside other metrics
What People Say
Adoption:
User Feedback:
Validation:
Limitations Noted: