I’m going to assume you already know about training with hearth rate zones. If you don’t know how this system works check out the site of Polar – why train with a hearth rate monitor. The hearth rate is used to tell us the “current intensity” of our training. While this system proves to be a pretty good indicator there are a few reasons not to base your training on hearth rate zones.

Hearth rate can be raised or lowered by “stress” alone. Stress can be fear, excitement, worries and many other mental or physical (such as illness or pain) factors. This makes hearth rate “not a constant factor”. You would not be able to measure properly if your ruler kept changing the length of a meter.

Hearth rate is also very difficult to calculate. You have to determine your maximum hearth rate which you will need to set your personal hearth rate zones. This can be a major problem. There a many formula’s to calculate your maximum hearth rate. Some of these come pretty close, but not a single one will give you an exact match. Only way to determine your maximum hearth rate is by undergoing a test. Then you will have to do such a test regularly, these tests aren’t very cheap.

So current hearth rate zone is influenced by “stress” AND “wrong maxHR”.

PZI – Pace Zone Index

Now here is where the pace zone index comes around. Instead of hearth rate zones you base your training on “tempo”. At a few given points during your training you do a test and based on this result you can set tempo values for different pace zones. The pace zone index system is an invention of Matt Fitzgerald and used by trainingpeaks.com. A full detailed summary on the Pace Zone Index system can be found right here. A detailed explanation of each Pace Zone can be found right here.

Wil this make hearth rate and there zones absolute? No! This still remains a very good indication of your fitness and the intensity of your run. Even better if you are interesting in knowing “how intense” your past or next workout is going to be it’s best done on hearth rate data. You can compare hr data against other training sessions to see if you your hr got lower or higher … if you got fitter and better.


I hope I explained a bit why you should base your training around “tempo” rather than “HR”.

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