Breathing is the only metabolic process you can consciously control — and most cyclists never think about it. Proper respiratory mechanics can lower your perceived effort at the same power output, delay the onset of diaphragm fatigue during hard efforts, and improve your CO2 tolerance so you stay composed when the road tilts up. The basics: learn to breathe with your diaphragm, match your breathing rhythm to your effort, and consider dedicated respiratory training if you're serious about marginal gains.
Most of us start cycling and just breathe however our body decides. That works fine until it doesn't — until you're three minutes into a VO2max interval and your breathing is so ragged it's the limiter, not your legs. This guide covers the respiratory mechanics that actually matter for cycling performance, drawn from conversations with Dr Andrew Sellars and TJ Eisenhart on the Roadman Cycling Podcast, plus the latest research on ventilatory training from the pro peloton.
In this guide:
- How breathing limits cycling performance
- Nasal vs mouth breathing: what the evidence says
- Diaphragmatic breathing for cyclists
- Breathing patterns by effort zone
- CO2 tolerance training
- Respiratory muscle training devices
- What the experts say
- Frequently asked questions
How Breathing Limits Cycling Performance
Here's the thing nobody tells you about hard efforts: your diaphragm is a skeletal muscle that fatigues just like your quads. When it fatigues, your body redirects blood flow away from your legs to keep the diaphragm working. The result is a measurable drop in leg power — not because your legs are done, but because your breathing muscles stole their blood supply.
This is called the respiratory metaboreflex, and it kicks in hard during sustained efforts above threshold. Research shows that diaphragm fatigue can reduce leg blood flow by up to 7% during maximal exercise. For a cyclist holding 300 watts, that's the difference between holding the wheel and getting dropped.
The good news: the diaphragm responds to training. Stronger respiratory muscles fatigue later, trigger the metaboreflex later, and keep more blood flowing to your legs when it matters.
→ Read the full guide: Breathing for Cyclists: Respiratory Training Guide
Nasal vs Mouth Breathing: What the Evidence Says
The nasal breathing conversation has exploded in the last few years. Let me break this down, because the answer is less binary than social media suggests.
Nasal breathing advantages:
- Produces nitric oxide in the nasal passages, which dilates blood vessels and improves oxygen delivery
- Warms and humidifies air before it reaches the lungs
- Naturally limits effort to aerobic intensities — useful as a Zone 2 enforcer
- Encourages diaphragmatic over chest breathing
When mouth breathing is necessary:
- Any effort above roughly 60-70% of VO2max — you simply cannot move enough air through your nose
- Racing, hard group rides, intervals above threshold
- Hot conditions where ventilatory demand increases
The practical takeaway: use nasal breathing as a tool for easy rides and warm-ups. It's an excellent way to enforce genuine Zone 2 pace — if you can't hold nasal breathing, you're probably riding too hard for a recovery or base day. But the moment effort rises above moderate, your mouth needs to be involved. Trying to force nasal breathing at threshold is fighting physiology.
| Effort Level | Breathing Approach |
|---|---|
| Zone 1-2 (recovery/endurance) | Nasal breathing — use it as an intensity governor |
| Zone 3 (tempo) | Mixed — inhale through nose, exhale through mouth |
| Zone 4-5 (threshold/VO2max) | Mouth breathing — maximise air volume |
| Sprint/anaerobic | Mouth breathing — everything you've got |
→ Read the full guide: Breathing Techniques for Cycling Performance → Read the full guide: Cycling Breathing Techniques
Diaphragmatic Breathing for Cyclists
Most people breathe with their chest — shallow, fast, inefficient. Cyclists make this worse by hunching over the bars, compressing the diaphragm, and defaulting to upper-chest breathing where lung volume is smallest.
Diaphragmatic breathing means using the dome-shaped muscle at the base of your ribcage to pull air deep into the lower lobes of your lungs, where gas exchange is most efficient.
How to practise it off the bike:
- Lie on your back, one hand on your chest, one on your belly.
- Breathe in through your nose — the belly hand should rise first and most. The chest hand should barely move.
- Exhale slowly through pursed lips. The belly drops.
- Do 5 minutes daily for 2 weeks before trying it on the bike.
On the bike: the aero position makes this harder, which is precisely why it matters. Focus on expanding your belly laterally against your hip flexors rather than trying to push it downward. Think "breathe into your sides" rather than "breathe into your stomach". In a good aero position, you can increase tidal volume by 10-15% with proper diaphragmatic technique versus upper-chest breathing.
→ Read the full guide: Breathing for Cyclists: Respiratory Training Guide
Breathing Patterns by Effort Zone
Rhythmic breathing — synchronising your inhale and exhale to your pedal stroke — reduces the energy cost of breathing and helps maintain a steady effort. The pattern shifts as intensity rises:
| Effort Zone | Breathing Rhythm | Notes |
|---|---|---|
| Zone 2 endurance | 3:3 (inhale 3 pedal strokes, exhale 3) | Relaxed, nasal if possible |
| Tempo | 2:2 or 2:3 | Mixed nasal/mouth |
| Threshold | 2:1 or 2:2 | Mouth breathing, controlled |
| VO2max | 1:1 | Rapid, deep, maximise ventilation |
| Climbing (seated) | 2:2, synced with pedal strokes | Focus on exhale — the inhale takes care of itself |
| Climbing (standing) | Match upper body rock | Use the natural compression of each pedal stroke to drive exhale |
The key insight from Dr Andrew Sellars on the podcast: most cyclists focus on the inhale, but the exhale is what matters. A complete exhale empties stale CO2-rich air from the lungs and makes room for fresh oxygen-rich air on the next breath. When you feel panicked on a climb, your instinct is to gasp in more air. The fix is the opposite — blow out harder.
CO2 Tolerance Training
CO2 tolerance is your ability to function with elevated carbon dioxide levels in your blood. Higher CO2 tolerance means you stay calm and controlled at intensities where other riders start gasping and panicking.
Dr Andrew Sellars explained this clearly on the podcast: the urge to breathe isn't driven by low oxygen — it's driven by rising CO2. Train your tolerance to CO2, and the desperate need to breathe arrives later and less intensely.
Simple CO2 tolerance test (do this at rest): Take a normal breath in, then exhale and time how long until you feel the first urge to inhale. Under 20 seconds suggests poor CO2 tolerance. 30-40 seconds is good. Over 40 is excellent.
Training protocols:
- Box breathing: Inhale 4 seconds, hold 4, exhale 4, hold 4. Progress by extending the hold phases.
- Extended exhale: Inhale normally, exhale over 8-10 seconds. Do 10-15 repetitions.
- Breath holds during easy rides: On Zone 2 rides, practise exhale-hold for 10-15 seconds every few minutes. Build tolerance gradually.
Team Visma-Lease a Bike has invested heavily in ventilation training and breathing sensor technology for their riders. When a WorldTour team allocates resources to respiratory efficiency, it tells you something about where the marginal gains still live.
→ Read the full guide: Andrew Sellars: Breathing, CO2, and Cycling → Read the full guide: Team Visma Breathing Sensor and Ventilation Training
Respiratory Muscle Training Devices
Inspiratory muscle training (IMT) devices — like the POWERbreathe and Airofit — add resistance to your breathing muscles, much like lifting weights for your diaphragm.
What the research shows:
- 6-8 weeks of consistent IMT (30 breaths, twice daily) can improve inspiratory muscle strength by 20-40%
- Time trial performance improvements of 2-4% in trained cyclists
- Reduced perception of breathlessness at the same power output
- Delayed onset of the respiratory metaboreflex
Practical protocol:
| Parameter | Recommendation |
|---|---|
| Device | Any calibrated IMT device (POWERbreathe, Airofit, or equivalent) |
| Resistance | 50-70% of maximal inspiratory pressure |
| Reps | 30 breaths per session |
| Frequency | Twice daily, at least 5 days per week |
| Duration | Minimum 6 weeks to see measurable results |
| Maintenance | 1 session daily after the initial block |
This isn't a must-have for every cyclist. If you're training 6 hours a week and sleeping 5 hours a night, fix the sleep first. But for the serious amateur who has the basics dialled and wants a genuine physiological edge, respiratory muscle training has better evidence behind it than most supplements.
→ Read the full guide: Breathing Techniques for Cycling Performance
What the Experts Say
The insights behind this guide come from direct conversations on the Roadman Cycling Podcast:
- Dr Andrew Sellars — breathing and respiratory performance specialist — on CO2 tolerance, nasal breathing as a training tool, and why the exhale matters more than the inhale.
- TJ Eisenhart — former professional cyclist — on how breathwork and meditation transformed his riding and his relationship with suffering on the bike.
Both conversations changed how we think about breathing inside the Not Done Yet community. The members who've adopted even basic diaphragmatic breathing and CO2 tolerance work consistently report lower RPE at the same power — and calmer efforts on climbs.
→ Hear the conversations: All Podcast Guests
Frequently Asked Questions
Should I breathe through my nose or mouth while cycling? Both, depending on intensity. Nasal breathing is a useful tool for easy rides — it enforces genuine Zone 2 pace and improves nitric oxide production. But above about 65-70% of VO2max, you cannot move enough air through your nose alone. Mouth breathing is essential for any hard effort. The practical approach: nasal on warm-ups and recovery rides, mouth opens as intensity rises.
Does breathing training actually improve cycling performance? Yes, with caveats. Inspiratory muscle training devices have 6-8 weeks of consistent use behind the evidence showing 2-4% time trial improvements. CO2 tolerance training and diaphragmatic breathing practice also show measurable benefits. But these are marginal gains — they matter most once your training structure, sleep, and nutrition are already solid.
What is CO2 tolerance training and why does it matter? CO2 tolerance is your ability to stay composed as carbon dioxide builds in your blood during hard efforts. The urge to gasp isn't triggered by lack of oxygen — it's triggered by rising CO2. Training your tolerance (through box breathing, extended exhales, and controlled breath holds) delays that panic response, keeping you smoother and more efficient when the pace goes up.
How do I breathe better on climbs? Focus on the exhale — blow out forcefully and let the inhale happen naturally. Most climbers make the mistake of gasping for air in, when the problem is stale air trapped in the lungs. Sync your breathing to your pedal stroke (typically 2:2 at threshold effort), and if you're standing, use the natural rhythm of your body rocking to drive the exhale. Drop your shoulders — tension in the upper body restricts ribcage expansion and wastes energy.
Can I use nasal breathing to train my Zone 2? Absolutely — it's one of the best self-limiting tools available. If you can sustain nasal breathing, you're almost certainly in Zone 2 or below. The moment you need to open your mouth, you've crossed into a higher intensity. It's not a perfect proxy for heart rate or power, but it's remarkably close for most people and costs nothing.
How long before I see results from respiratory training? Most studies show measurable improvements in inspiratory muscle strength within 4-6 weeks of consistent training (30 breaths, twice daily). Performance benefits — lower RPE, improved time trial power — typically appear by 6-8 weeks. CO2 tolerance can improve faster with daily practice, sometimes within 2-3 weeks.