Exercise intensity zones can be defined using the talk test, RPE, or heart rate monitors.

“I think what's cool about having all these different metrics to define the zones is that you know if people don't really want to train using heart rate or maybe they don't even have a heart rate monitor they can use the talk test they can use RP or maybe a combination of all three of these and they're pretty reliable I mean they've all of these have been kind of well evidenced to correspond to the different zones but I think what's nice is that people can use these to train and it doesn't require a lot of technical ability a lot of experience”