The Paradox of Going Slow
When I first heard that elite endurance athletes spend 80% of their training time at low intensity, I assumed they were holding back. Pacing themselves for race day.
I was wrong. They train slow to get fast. The science behind this seems counterintuitive until you understand what's happening in your cells.
Mitochondria: Your Cellular Engines
Mitochondria are the power plants of your cells. They take oxygen and fuel and produce ATP—the energy currency your body runs on. The more mitochondria you have, and the more efficient they are, the better you perform at everything.
Zone 2 training—that pace where you can talk but it's slightly strained—specifically optimizes mitochondrial function. It trains your Type 1 muscle fibers to burn fat efficiently and clear lactate. This is the foundation that everything else builds on.
The "Gray Zone" Mistake
Here's where most people go wrong: they train too hard on their easy days and not hard enough on their hard days. They end up in what coaches call the "gray zone"—Zone 3.
This intensity is too hard to build aerobic base efficiently but too easy to build speed and power. It's the worst of both worlds. You accumulate fatigue without getting the benefits of either approach.
- True easy days: You should be able to hold a conversation without gasping. It should feel almost too easy.
- True hard days: You should be working near your limits. Uncomfortable. Focused.
Most people reverse this. They go medium-hard every time and wonder why they plateau.
What Zone 2 Feels Like
Zone 2 training should feel sustainable. Almost pleasant. Like you could keep going for hours (and eventually, you should be able to).
Heart rate is typically 60-70% of max, roughly speaking. But the best indicator is conversation ability. Can you talk? In complete sentences? Without gasping? Good. You're in the zone.
A 45-60 minute Zone 2 session—cycling, jogging, rowing, even brisk walking—is one of the best investments in your metabolic health. Do 3-4 of these per week, add one hard session, and watch what happens over months.
The Long Game
This approach requires patience. You won't see changes in a week. But over months and years, your aerobic base grows. Your resting heart rate drops. Your body becomes better at burning fat. You recover faster. And when you do go hard, you can actually push harder because you're coming in fresh.
Sometimes slowing down is the fastest way forward.