Updated: Apr 17, 2020
Training by HR can be a smart technique to guide your intensity during training. It can really help make your easy workouts easier, your hard workouts harder and ensure that you are working at the right intensity.
Finding your zones
Currently the best formula for finding your max HR is 208 - (0.7xage) if you haven't been tested in a lab. The visual below has established zones in relation to Lactate Threshold from a runner. These are the same zones that you would extract from your max HR, although this is more specific to this individual.
Each HR zone serves a purpose in your training (as the visual shows). WAYYY too many runners spend too much time in the middle of the road intensities. This is actually holding you back from reaching your potential.
With polarised training you can dramatically improve. The key is to train in all of these zones at different times to maximize performance. The time devoted to each zone is event specific and dependent on your goals.
Let's not forget training by perception of effort is still the number one feedback mechanism. Albeit a skill that develops with experience. Make sure to invest in a good HR chest strap if you do intend to use this method. Also make sure to discus with a professional coach if necessary.