Respiratory Scientist: How To Breathe So Running Feels Easier | Dr. Andrew Sellars

Can your breathing be the hidden reason running feels harder than it should?

In this episode of The Endurance Lab, I sit down with Dr. Andrew Sellars to explore one of the most overlooked performance limiters in endurance sport: breathing.

Most runners focus on aerobic fitness, mileage, and strength training — but almost nobody trains the muscles that power every breath. Dr. Sellars explains how inefficient breathing can quietly drain performance, why the respiratory system may be the bottleneck for many runners, and how targeted breathing training can improve running economy, VO2 max, and overall endurance.

We talk about how the respiratory muscles affect performance, why breathing may decline with age if left untrained, and how runners can improve it without adding more mileage. We also dive into CO2 tolerance, nasal vs mouth breathing, respiratory muscle training, and how breathing patterns can influence how hard running feels at marathon pace and beyond.

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In this episode, we cover:

• Why breathing is often ignored in endurance training

• How the respiratory system can limit running performance

• Why breathing can use up a significant amount of energy during hard efforts

• The role of respiratory muscles in fatigue

• Whether breathing gets worse with age

• CO2 tolerance and why it matters for runners

• How respiratory muscle training works

• How breathing affects VO2 max

• Nasal breathing vs mouth breathing for runners

• Why slower, deeper breathing may help running feel easier

• How to integrate breathing training into marathon prep

Chapters

00:00 Intro

00:40 Who Is Dr. Andrew Sellars?2:15 Is Breathing Limiting Your Running?

7:26 How Does Breathing Limit Performance?

10:43 What Actually Limits Your Breathing?

16:08 The Low-Hanging Fruit Most Runners Ignore

18:08 What Is CO₂ Tolerance?

25:45 How To Improve CO₂ Tolerance?

29:41 What is Respiratory Muscle Training?

34:438 How Much Faster Can Breathing Training Make You?

41:37 Can Respiratory Muscle Training Improve VO₂ Max?

47:07 How Would Respiratory Muscle Training Fit Into A Training Plan?

57:013 The Best Breathing Pattern for Marathon Pace

01:02:14 Nasal vs Mouth Breathing

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