Zone 2 is low-intensity cardio done at the hardest pace you can hold while still speaking in full sentences. Physiologically, it sits just below your first lactate threshold, which lands around 60 to 70 percent of max heart rate for most people. Blood lactate stays low, slow-twitch muscle fibers do the work, and you could keep going for an hour without falling apart.
Why it matters
Zone 2 is where you build your aerobic engine. Easy, steady work grows mitochondria in slow-twitch fibers, and that improves fat burning, endurance, and how fast you recover between hard efforts. Elite endurance athletes spend roughly 80 percent of their training time here. Not because they're lazy. Because the research shows that mix beats grinding at moderate intensity every session. Most people ride their easy days too hard, so they never collect the adaptation.
How to use it in training
Start with two or three sessions a week, 30 to 45 minutes each. Incline walking, easy cycling, light jogging, a rower at conversation pace. Anything steady works.
Use the talk test. Full sentences should be comfortable, but singing would be a stretch. A heart rate target of 60 to 70 percent of max is a decent backup check. And resist the urge to speed up. Going harder doesn't make a zone 2 session better, it makes it a different workout.
Related terms
Go deeper
Want the actual studies behind all of this? Read our full breakdown: Zone 2 training research.