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Dr Andrew Sellars has spent 35 years studying why cyclists blow up on hard efforts. His answer: it's not your legs, it's not your heart. It's your breathing. And the French study he references on this episode of the Roadman Cycling Podcast showed pro cyclists improving FTP by 6% over 48 weeks purely through respiratory training protocols.
The main thing Sellars told me that I hadn't heard before is that CO2 drives your breathing, not oxygen. The harder you ride, the more CO2 you produce, and your body has to breathe faster to blow it off. Your blood oxygen level barely moves. Which means when you can't hold your power on a hard effort, your breathing system may have given out before your legs did. Sellars says most athletes have never trained this system at all, which means there's a meaningful gain sitting there untouched.
The protocol from the French study Sellars references ran 48 weeks and broke down into six-week blocks: diaphragmatic breathing and nasal breathing first, then coordination work, then resistance training, then aero-position-specific breathing. The pro cyclists in that cohort increased tidal volume from 6.5L to 7.7L, a 10% improvement, and averaged 6-8% FTP gains. Sellars also says nasal breathing stimulates the opposite hemidiaphragm, so breathing through your right nostril activates your left hemidiaphragm, which increases diaphragmatic involvement compared to mouth breathing. And slower breathing improves HRV by allowing greater cardiac stretch between beats, which is why Marco Altini says breath control during HRV measurement is so important.
If you want to understand how HRV actually works and why wrist-based devices give you bad numbers, go listen to the Marco Altini episode. And if your heart rate is running higher than expected at a given power output, the five fixable reasons episode is worth your time.
A French study referenced by Dr Sellars showed professional cyclists improving FTP by approximately 6% over 48 weeks through structured respiratory training — a magnitude that exceeds typical adaptation gains from training-load increases alone in already-trained pros.
Source: Dr Andrew Sellars, citing French respiratory training research
Sellars improved his run pace from approximately 6:30/km to sub-4:00/km over 6 weeks of slow-breathing-pattern training as a 19-year-old triathlete in 1989-90 — using 8-track cassette tapes on yoga breathing patterns as the protocol.
Source: Dr Andrew Sellars first-person account
Carbohydrate sources during cycling fueling affect respiratory pattern independently of blood glucose response — Anthony's Timeware data showed Haribo jelly consumption produced a measurable shift in breathing rate and RPE on the same wattage compared to other carbohydrate sources.
Source: Anthony Walsh, on the Roadman Cycling Podcast (Timeware data)
The Timeware respiratory wearable measures breathing frequency and provides directionally useful (not absolutely precise) breath volume data — its primary value is in pattern awareness, which Sellars considers a prerequisite for trained respiratory adaptation.
Source: Dr Andrew Sellars, hands-on with Timeware product
“The main reason you breathe faster with higher intensity exercise is to blow off CO2, which is a byproduct of metabolism. So the harder you work, the more CO2 you produce, the harder you have to breathe to blow it off.”
“If you rebreathe some CO2, you can balance your physiology. And now you can actually train your breathing for as long and hard as you want without actually negatively affecting your physiology and without having to drive the body to levels that would be really hard to mimic a race without riding really really hard.”
“That brilliant book, but it really should have been called the CO2 advantage, the carbon dioxide advantage, because all of the the entire book is about this understanding of what happens to your body with higher levels of CO2 and the physiologic benefits of higher levels of CO2 if you can tolerate it.”
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