Zone 3 Confusion & the Fatigue-Equals-Fitness Trap
A common mistake in endurance training is equating effort with progress. In reality, not much intensity is required.
Responding to my training advice for a skimo vertical, a Redditor asked for clarification on when "intensity" starts. (At aerobic threshold, not anaerobic.) I offer five ways to find it.
Where does intensity begin?
...when you mention 5% [for a 2-hour event], you mean at or above LT2 right? For zone 3 (or in between thresholds) we could do up to around 15%-20% ?
Intensity starts at aerobic threshold.
By "intensity", I mean anything above aerobic threshold (AeT), not anaerobic threshold (AnT).
The gap between the two—aka. Zone 3—is very individual and based on training history. Someone who has spent too much time in Z3 will have a wide gap, while someone with a well-developed aerobic system will have a narrow one. (The worst I've seen is over 30%; the best, less than 5%.)
If you don't know your AeT, you could:
- Do Scott Johnston's drift test;
- Get a proper lab test done by a knowledgeable tech (but buyer beware);
- Try Tymewear (excellent, but the sensor is expensive);
- Guess at 80% of AnT (not great, but most training volume will always be less than that anyway); or
- Super worst-case: ignore reality and associate effort with progress, and fatigue with fitness.
Number five is the most popular—and the most destructive for fitness.