How it works
You spend most of your training time easy, below your first threshold (roughly Zone 2). The body grows mitochondria, adds capillaries, and improves fat oxidation to spare glycogen. These adaptations raise the speed and power you can hold aerobically.
The Lydiard tradition
New Zealand coach Arthur Lydiard popularized periodizing a season as base first, then sharpening. Athletes log a long block of high aerobic mileage before layering on hills, tempo and speed. Speed work is more effective, and safer, on a deep base.
How to apply it
Keep easy days easy. The most common mistake is letting Zone 2 drift into Zone 3, which blunts the adaptation and adds fatigue. Anchor intensity to heart rate (a Zone 2 cap or Maffetone's MAF method) and build volume gradually.
FAQ
How long does it take to build an aerobic base?
Building an aerobic base takes months and seasons, not weeks. Mitochondrial and capillary adaptations accumulate slowly with consistent easy volume. The deepest bases are built over years.
Why do I have to go so slow?
Easy aerobic intensity triggers the adaptations (fat oxidation, capillarization, mitochondrial density) that raise your aerobic ceiling. Going harder shifts the stimulus and adds fatigue without improving the base. Slow running is the core skill of base training.
How is aerobic base training related to MAF and Zone 2?
They overlap heavily. Zone 2 is the easy aerobic band. Phil Maffetone's MAF method sets a heart-rate cap (around 180 minus your age) to keep you in it. Both keep base work easy enough to do its job.