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We focus on aerobic base training mainly because it’s safer and more sustainable for long-term improvement. It’s not so much about your heart rate going over a certain number, like your max heart rate or dipping into Zone 3, that’s the issue. The bigger concern is the stress on your musculoskeletal system: your tendons, bones, and ligaments. These tissues are more fragile and take longer to adapt than your cardiovascular system.
When runners train too fast on easy days, slipping into Zone 3 or Zone 4 instead of staying in Zone 2, they increase the impact forces with every step. That added stress can lead to overtraining or injury.
There’s also the mental side. It’s exhausting to push hard and experience discomfort every day. You don’t want that imbalance in your training as both your body and mind need easier days to recover and adapt!
The third and final reason we emphasize Zone 2, low-intensity running is consistency. When you stay at a lower intensity, you’re less likely to get injured, and it’s mentally easier to keep showing up day after day. That consistency allows you to build more total volume- running longer, covering more distance, and training more frequently.
And that’s where the balance comes in. Higher-intensity running actually creates a stronger stimulus for many aerobic adaptations. Things like increased mitochondrial density, improved running economy, and higher VO₂ max. But because those harder efforts take more out of you, they can’t be done every day. Lower-intensity running lets you train more consistently and build the overall volume that supports those adaptations and makes the harder sessions more effective.
The beauty of lower-intensity, aerobic-based training is that it lets you run more, more often, and more consistently and that’s what truly makes you a stronger, faster, and more efficient runner.