There are five main training zones according to the American College of Sports Medicine (ACSM): Zone 1: Less than 57% of your heart rate max. This zone includes relaxed activities or warm-ups. Zone 2: 57-65% of your heart rate max. Still rather relaxed activities, but something like a nice walk or even a light jog for more conditioned people would likely be Zone 2. Zone 3: 65-76% of your heart rate max. This is where things start to get a little more fun. You’re working up a sweat and starting to breathe a little harder, but this is an activity you can maintain for quite a while. Zone 4: 76-95% of your heart rate max. Zone 4 is wide but presents a good portion of most intense training. A good portion of your normal running, biking, swimming, etc., will likely land in the lower area of Zone 4. As you reach the upper end, you’re pushing pretty hard. Zone 5: 95%+ of your heart rate max. This is an all-out effort. You’re in this zone to set PRs and maybe vomit—possibly both! Most people can only sustain activity for up to a few minutes in Zone 5.