Base training explained: how to build your aerobic engine

Base training is the least glamorous and most important phase of any endurance plan. It is where you build the aerobic engine that everything else runs on. Here is what it is and how to do it right.

What base training actually builds

Easy aerobic riding and running drives adaptations you cannot get from intervals: more capillaries, bigger mitochondria, better fat metabolism, a stronger heart. These take weeks of consistent, low-intensity volume — there is no shortcut.

How easy is easy?

Most of your base should be genuinely easy — conversational pace, low heart rate. The classic mistake is riding base too hard, turning easy days into medium ones. That builds fatigue without the deep aerobic adaptations. Track it with TSS so easy stays easy.

How long should a base phase be?

Typically 6–12 weeks, depending on your event and starting point. Volume rises gradually — add no more than about 10% per week — with a recovery week every 3–4 weeks. Your Fitness (CTL) should climb steadily; if fatigue spikes, you are going too hard.

When to move on

Once your aerobic base is solid, intensity in the build phase turns that engine into speed. Build too early on a weak base and you plateau fast. Watch your Fitness and Form to know when the base is ready. TrainCurve tracks it automatically — start free.