Concept
Zone 3
A moderate aerobic intensity above easy running that creates more training stimulus and more recovery cost.
What Zone 3 feels like
Breathing is clearly stronger and conversation becomes limited, but the effort remains controlled rather than maximal.
Where it can help
Planned steady or race-specific work can use moderate intensity when it serves a clear phase and goal.
Why it can become a trap
Running moderately hard every day is too demanding to accumulate easy volume and often too easy to replace deliberate quality work.
How to use it
Use Zone 3 intentionally, label its purpose, and protect genuinely easy days around it.
Common misconception
Zone 3 is not useless, but accidentally turning every easy run into Zone 3 usually creates unnecessary fatigue.