I’ve been seeing a lot of talk recently about zone 2 running. In a way, this is wonderful. In a way, this is a bit troubling.
Why? Well, it’s wonderful because people are talking about keeping easy runs easy. This is so important. A majority, even significant majority, of your time spent running should be at an easy pace.
So why is it a bit troubling? Mainly because people are failing to define what they mean by zone 2.
There are a couple primary problems here.
First, zone 2 of what? I’ve seen anything from 3 zone models to 7 zone models. Obviously, zone 2 in a 3 zone model is going to be quite a bit different than zone 2 in a 7 zone model.
Ok, so let’s split the difference and go with the probably most used 5 zone model. Wonderful, we have a clear definition of what model we’re using and what zone 2 is, right? Well, see the images at the top of this post. Those are from the same run. According to one 5 zone model, 99.7% of a recent long run I did was in zone 2. Fabulous! I nailed it! But the other model only had 36% of my run in zone 2. Oh no! I ran way too easy!
How did this happen? Well, two keys are right in those images.
My zone 2 according to one model is 117-145 beats per minute. According to the other model, it’s 136-151 beats per minute. In other words, even within the paradigm of 5 zone models, you can see significant differences in what zone 2 is.
The second problem displayed is that the models are using a different max heart rate. Note that, even if they had the same max heart rate, their definitions of zone 2 would be different. However, if you don’t have an accurate max heart rate, you’re going to further distort these numbers. The big problem here is that most people don’t know what their max heart rate is. The best they can do is come up with a close approximation but even a close approximation means there is some error in the zones.
Even further, I’ve seen some people who panic when not 100% of a run is within the zone. 99.7% of the run was in zone 2? Not enough. Fail. All I can say to that is please don’t be so strict on yourself.
Again, I strongly believe encouraging zone 2 is well intentioned and conceptually a good idea. It’s important to not run your easy runs too hard. However, there are better ways. I’ve written previously about conversational pace, something that might not be as set in stone but gives you the flexibility that your body needs. As we’ve seen above, heart rate zones aren’t set in stone anyway and, once you pick one, it’s not flexible enough to account for things like dead legs or a higher or lower than normal heart rate not due to effort but possibly due to things like fatigue from lack of sleep or high stress or the caffeine from the two cups of coffee you had right before the start of the run.