Why You’re Slowing Down Even When You’re Fit.

G'day mate,

As I train for the Berlin Marathon, I’ve been diving deeper into what it really takes to stay strong across 2, 3, or even 4+ hours of work. That’s where Brady Holmer comes in.

Brady has a Master’s in Human Performance and translates the latest science in exercise, nutrition, and longevity into real-world strategies. He also runs a 2:24 marathon! I’ve been learning a ton from him and I’m stoked to share his guest post with you today.

He’s breaking down a concept called physiological resilience. If you’re like me and want better endurance, this is gold.

In this week’s Newsletter (6 min read):

🧬 The 3 classic pillars of endurance—and the new “missing link”

⏱️ Why your pace feels harder late in a race (even if it isn’t faster)

🏋️ Proven ways to train your physiological resilience

If your mate wants to run faster for longer, share this link with them. Make sure they subscribe to earn a prize!

Now over to Brady 👇

🧠 The 3 Pillars of Endurance (and What They Miss)

Back in the 1990s, physiologist Dr. Michael Joyner introduced a now-famous model for endurance performance. It’s built around three core traits:

1. VO₂max – the maximum amount of oxygen your body can use

2. Running economy – how efficiently you move at a given pace

3. Lactate threshold – how close to your VO₂max you can operate for long periods

These are foundational—but here’s the problem: they assume your performance stays consistent from start to finish. Anyone who’s run a marathon knows that’s not how it goes.

💥 Enter: The Fourth Pillar — Resilience

Physiological resilience, also called durability, refers to how well your body resists fatigue-related decline over time. 

It became a hot topic after Nike’s 2017 Breaking 2 project and is now considered the missing link in endurance performance. It addresses how athletes maintain performance as fatigue accumulates, beyond initial physiological capacities. 

It’s not about mental grit, it’s about how your VO₂max, economy, and lactate threshold shift under fatigue. Even if you start fresh and fit, you may fade fast. 

In studies, critical speed (the pace you can hold indefinitely before fatigue sets in) has been shown to drop by 10% or more after a couple hours of intense effort. But the decline varies a lot:

• Highly resilient athletes may lose just 1–2%

• Others lose 25–30%

And here's the wild part: the fastest and fittest runners aren’t always the most resilient! That’s why this “fourth pillar” is so important—it fills the gap that traditional models miss.

🧪 What Causes Performance Decline Over Time?

Fatigue isn’t random. There are real, well-understood mechanisms behind it. Here’s what’s happening:

1. Fuel shifts – You burn more fat as glycogen runs low, which requires more oxygen.

2. Muscle fiber recruitment – You lose access to efficient slow-twitch fibers and start using faster-fatiguing ones.

3. Blood volume drops – Sweat reduces cardiac output and oxygen delivery.

4. Form breaks down – Biomechanics become less efficient, raising energy cost.

5. Heat and humidity amplify it all – Higher temps speed up glycogen use and fatigue.

Over time, these stressors pile up, increasing perceived effort and pushing you into the dreaded “wall.”

The end result? That same pace from mile 3 feels way harder at mile 23.

🧱 How to Train Resilience

Resilience may not be as flashy as VO₂max, but it’s just as trainable:

• Build your aerobic base – Higher weekly mileage over time improves durability.

• Run under fatigue – Include fast-finish long runs, threshold sessions, and marathon-pace efforts late in workouts.

• Strength train – Heavy lifts and plyometrics improve economy and delay fatigue.

• Fuel well – Aim for 60g+ of carbs/hour in long races or workouts to maintain critical power and delay the wall.

Take Eliud Kipchoge’s sub-2:00 marathon for example. It wasn’t just about speed—it was about not slowing down. He ran negative splits and held pace when most would fade.

His resilience likely comes from:

• Decades of consistent high-volume training

• Smart fueling and pacing

• Possibly some biomechanical or metabolic advantages

Whatever the reason, he slows down less. And that’s what makes the difference.

🎯 Final Takeaway

If you've ever trained hard but still struggled in the second half of a race, this is the missing piece.

Improving resilience might not increase your VO₂max, but it will help you slow down less. And slowing down less… is another way of saying you’ll race faster.

I think it’s important for all of us to think about resilience not just in our athletic life, but also in our personal lives. We need to be robust against the mental and physical stresses of everyday life so that they don’t break us down. If we’re successful, we can take a life lesson from Eliud Kipchoge and learn that “no human is limited.”

🙌 From Brady

A huge thanks to Dan for letting me write this guest post and share a topic I’m excited about. If you liked this post, subscribe to my newsletter Physiologically Speaking where I write about similar topics weekly.

You can also find me on X and Instagram:

X: b_holmer - https://x.com/B_Holmer

Instagram: @brady.j.holmer - https://www.instagram.com/brady.j.holmer/?hl=en 

Quick Notes (From Dan)

💪 Huge shoutout to Brady for sharing this post with us. I learn so much from him behind the scenes, so I’m stoked to have him share a bit of his wealth of knowledge with us on Legendary. Make sure to SUBSCRIBE to Physiologically Speaking and follow him on Instagram and X—his content is top-tier.

💚There’s a big announcement from us at AG1 coming tomorrow!!! Stay tuned.

🎬 New YouTube video is out: Hyrox training with 3x world champion and my good mate Hunter McIntyre. WATCH HERE.

#EatGoodFeelGood

DC