What heart-rate zones actually are (and why they matter)

Every workout you do lives somewhere on a scale from a gentle walk to an all-out sprint. Heart-rate zones turn that scale into five simple buckets, each defined as a percentage of your maximum heart rate.

Your max heart rate is roughly 220 minus your age. From there, Zone 1 sits at 50–60%, and each zone climbs ten points to Zone 5 at 90–100%. The point isn't to live in the red — it's to know which zone a session belongs in, and to spend your time there on purpose.

Lower zones build the aerobic base that everything else rests on. Higher zones sharpen speed and power, but you can only hold them for seconds to minutes. A good training week is mostly easy, with a little hard — and zones are how you keep that ratio honest.