About a year ago, I came across a podcast episode featuring Peter Attia and Iñigo San Millán, both medical professional experts in their field, where Peter focuses on life longevity and Iñigo on biological aspect of sports science. These two completely change the way I approach cycling. Before this, I believed that to improve, I had to push harder, go faster, and constantly test my limits, hit hard to go fast. Chase the KOMs, the climbs and the PRs.
It turns out, I was wrong.
Listening to that conversation between Peter and Iñigo opened my eyes to something I had been missing: Zone 2 training—the aerobic foundation that builds endurance and fatigue resistance in a way that high-intensity training simply can’t. They broke down the science, explained the benefits, and most importantly, showed me how to train smarter, not just harder. It was about building mitochondrial density and the science and data behind it.
Zone 2 is not just casual riding
Zone 2 training refers to a specific intensity of exercise where your body relies predominantly on fat as its primary fuel source. In terms of effort, it feels moderate—you should be able to carry on a conversation but still feel like you’re working. It has to be steady and long with minimal disruption. It’s not the all-out efforts that leave you gasping for air; instead, it’s a controlled, steady pace that helps you build your aerobic base. Stay out of the hills!
Why is this important? Because this is the zone where your body can efficiently burn fat, avoid excessive lactate buildup, and ultimately improve your endurance. The more time you spend training in Zone 2, the better your body becomes at burning fat for energy, which is crucial for long rides or races where endurance matters most. It forces your body to produce more mitos to burn fat and less glucose.
The Science Behind It
One of the biggest takeaways from the podcast was understanding how training in Zone 2 leads to an increase in mitochondrial density. Mitochondria are the powerhouses of your cells—they help your muscles use fat for fuel. The more mitochondria you have, the better your body can handle sustained efforts over long periods of time without burning out. This means you can keep going, ride longer, and feel less fatigued at the end of your efforts.
Iñigo explained that while high-intensity efforts burn carbohydrates (glucose) and produce lactate, which leads to muscle fatigue, training in Zone 2 allows your body to build its fat-burning capabilities and clear lactate efficiently. This ultimately leads to better endurance and fatigue resistance, which is exactly what we all want, especially when preparing for races.
My Own Training Shift
Before hearing this, I was stuck in a cycle of constantly pushing myself to the limit. I thought that was the only way to improve. I thought it was about raising my Vo2max and holding at those intensities, turns out that's not the case. Not entirely. But after learning about proper Zone 2, I made some major changes to my training plan.
It wasn’t easy at first—slowing down felt counterintuitive. And let’s be honest, it’s hard to hold back, especially on hills or when you feel like you should be going harder or when you're getting passed. But the more I stuck with it, the more I noticed improvements.
The Benefits I’ve Seen
Since I committed to regular Zone 2 training, the changes in my endurance have been remarkable. I can ride longer without feeling that crushing fatigue I used to experience. What’s more, I’ve learned to better pace myself during races and long rides. I can finish stronger and recover faster because I’m no longer burning through my glycogen stores too early.
One of the key adjustments I made was avoiding hills or backing off when I hit them during my Zone 2 rides. Steep climbs push your heart rate into a higher zone, shifting you out of fat-burning mode and into glucose-burning mode, which defeats the purpose of Zone 2 training. This was a tough habit to break, but it made a huge difference in keeping my efforts consistent. Man is it so hard to hold back when someone passes you!
The Importance of Consistency
One of the lessons I took away from Peter and Iñigo’s discussion is that Zone 2 training is about the long game. It’s not a quick fix; it’s something you need to do consistently over time to see real results. But it’s worth the patience.
I recently went through a hard down time, broke my pelvis and have been off the bike mostly for nearly 10 weeks. My threshold power dropped 100 watts. In the chart below, you can see the light blue line, my threshold power has increased significantly from 273 watts to 300 watts in a span of 3 weeks. By conditioning my body to use more mitos at low intensity and consistent volume, it has allowed me to grow my threshold power when I step on the gas.
Why You Should Try It
I’m not claiming to be an expert, but I’ve experienced firsthand the benefits of Zone 2 training. If you’re like I was—constantly pushing hard but feeling burned out or stuck—it might be time to rethink your approach. By focusing on training smarter rather than always going harder, you can build the endurance and efficiency that will make a difference in your performance.
Zone 2 might not be the most exciting or intense part of training, but it’s the foundation for everything else. It allows you to build a bigger engine that can handle the demands of long rides and races. And trust me, once you experience the benefits, you’ll wonder why you didn’t start sooner.
So if you haven’t already, give Zone 2 training a try. I highly encourage you to watch the podcast and see the data, it's seriously the most informative information about it you'll see. It might just be the game-changer you’ve been looking for, just like it was for me.
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