Zones are used to give an athlete a well defined training intensity at which they should be working to during an activity. They may, for example, be completing intervals at ‘zone 3’ for 20 minutes.
Training using zones is important because it means that riders can be sure they’re pushing hard enough during intervals, that they’re racing at a sustainable output for the duration required, and that they’re pedaling gently enough on recovery and endurance rides.
Zones can be based on Power, Heart rate or Pace (For runners).