I run three times a week. Am I already getting zone 2 benefits?

Running three times per week provides zone 2 benefit only if the runs are performed at zone 2 intensity, most recreational male runners in their 40s train in zone 3 or zone 4 (the "moderate-hard" range, too hard for zone 2 fat oxidation benefits, too easy for HIIT cardiovascular ceiling improvements), a common problem called the "grey zone" that produces less adaptation than either the easy or hard end of the spectrum (Seiler & Kjerland, Scand J Med Sci Sports, 2006).

This is the polarization principle: going harder on your easy days reduces adaptation compared to being genuinely easy (zone 2) while going hard enough on hard days to genuinely be zone 5 (90%+ HRmax). The grey zone (zone 3–4) is where men who "work hard" in their runs often spend most of their training time, too hard to build maximum fat oxidation base, not hard enough to generate the zone 5 VO2max stimulus. Check your training heart rate data from your last three runs. If they are all between 140–165 bpm (for a 45-year-old), you are in the grey zone.

Honesty Scale: Solid (1) for the polarization principle and grey zone inefficiency in endurance training.

What to do: Look at your last 10 runs' average heart rate. If your "easy" runs average above 140 bpm (at age 45), they are not zone 2, slow down. Add a GPS watch with heart rate to keep you disciplined in zone 2. It will feel frustratingly slow at first.

For the full picture, read The VO2max/Zone 2 Deep Dive