2. The 80/20 principle

Performance improves when about 80% of training time is spent at low intensity and 20% at higher intensity.

Playbook

1. Objective: Optimize training load distribution.
2. What to do: Classify each session as easy or hard.
3. How to do it: Track total time in each intensity zone, not just sessions.
4. Frequency: Each training cycle.
5. Progress indicator: Consistent alignment with the 80/20 ratio.
6. Common error: Making easy days harder than planned.

Generic mini caseA runner adjusts weekly training and sees race-pace improvements after several weeks.