Zone 2 refers to a heart-rate zone — roughly 60–70% of your maximum heart rate — at which the body relies primarily on fat oxidation rather than glucose for fuel. It has become a fixture of both elite endurance training and longevity-focused fitness advice.
Why it matters physiologically
Training consistently in Zone 2 improves mitochondrial density and efficiency — the cellular machinery responsible for aerobic energy production. Over time, this raises the intensity at which you can exercise while still burning fat as a primary fuel source, effectively raising your aerobic ceiling.
How to find your Zone 2
A rough estimate is 180 minus your age, adjusted down slightly for those newer to training. A simpler field test: you should be able to hold a full conversation, breathing through your nose, without needing to catch your breath between sentences.
What it isn’t good for
Zone 2 alone won’t build significant strength or top-end speed, and progress in aerobic capacity from Zone 2 work is slow and cumulative — measured in months, not weeks.
The bottom line
Zone 2 training is a long-game investment in aerobic health with strong physiological backing, best used alongside — not instead of — strength training and higher-intensity work.
