# Effective VO₂max in Runalyze is not a pure performance metric — it’s a heart-rate–based estimation that depends heavily on:
- HR vs. pace relationship
- Cardiac drift
- Fatigue / recovery state
- Environmental effects (heat, humidity, wind)
- Suboptimal HR values during easy runs (e.g., unusually high HR because of fatigue or stress)
On easy days, you are intentionally running much slower, but your HR may still be elevated due to fatigue, stress, or conditions.
-> This makes the algorithm think you are less efficient → lower Effective VO₂max.
# Why tempo runs and races give you much higher values
- Sustained tempo runs and races are far more stable indicators of your real aerobic capacity because:
- Pace/HR ratio becomes more linear at moderate–high intensities.
- You’re better warmed up and biomechanically efficient.
- External influences matter less compared to easy running.
- Your effort more closely reflects your current performance ability.
That’s why you get 46–50 in tempo sessions and around 50.5 during your last race — those are far better reflections of true VO₂max.
# What you can do
Adjust your correction factor via the Performance Status view. Have a look at this blog post:
https://blog.runalyze.com/features/new-view-for-your-running-performance-status/