What is the difference between zone 1 and zone 2? Between zone 4 and 5? Between 8 and 9?
What? You didn’t know there were 9 zones? What kind of crap is this!?!?!
As a coach and exercise physiologist, I’m often asked the differences and exact heart rate thresholds between zone 3 and 4, or 1 and 2, etc. “Well, my old coach said Z1 stopped at 143, and now you’re telling me it stops at 144? Which is right? Crap!”
The truth is, zones are crap. With one exception, zones are a totally arbitrary set of numbers, which is why there are literally dozens of ways to calculate “Your Zones.”
Everyone assumes that there is a physiological change that happens between each zone, and that training 1-2 beats higher or lower effs everything up. Simply not true.
The best way to understand how your body works is to think of a graded exercise test. Imagine you are on a treadmill, and every 60 seconds the speed and grade go up. Through this process, your heart rate, lactate readings and perceived effort level go up, and up, and up. The ONLY physiological change that happens between any of these different intensities is when you hit the point where your body can no longer clear as much lactate as it produces. This is technically called OBLA (the Onset of Blood Lactate Accumulation) which, for practical (and technically incorrect) purposes, we call the Lactate Threshold (LT).
Wait, if there’s only actually ONE physical event associated with an increase in intensity, how do we end up with three, four, five, or even nine zones? What do we use to demarcate the difference between say, Z1 and Z2? MAGIC. No, but seriously. We use math, which, since our body isn’t math, is basically friggin’ magic.
The most common way to set the zones is to “test” for max heart rate (VERY difficult to test in all but the most masochistic of athletes), and then use MATH to extrapolate zones. 60-70% is Z1, 70-80% is Z2, etc. Think your body cares whether your training at 68% or 72%? Unless your OBLA is at 70%, nope. .
The “proper” (because I said so) way to calculate your zones, is to test your Lactate Threshold Heart Rate (LTHR), or Functional Threshold Power (FTP). From there, you have the only two zones that matter, Under Threshold, and Above Threshold. This isn’t new info, physiologists have known this for years. So why all the friggin’ zones?
Let’s look at how we would develop a zone system. We know that we only have one number that’s really set, right? And that’s LT. Lets assume for this athlete that it’s 170bpm. That starts us with the following zones.
Z1: Under -Threshold: HR 120-170
Z2: Over-Threshold: HR 170-max
And we know that trained athlete usually recover better with easy efforts than sitting on their bony asses, so we want a nice easy training zone in there, so we have:
Z1: Easy: HR 120-140
Z2: Under-Threshold: HR 140-170
Z3: Over-Threshold: HR 170-max
Let’s say this athlete’s average HR during a race is 180. We know that we want to develop speed higher than race pace, so that race pace feels more comfortable. So we make a zone for that.
Z1: Easy: HR 120-140
Z2: Under-Threshold: HR 140-170
Z3: Over-Threshold: HR 170-190
Z4: Over-Speed: HR 190-max
Annnd, lets say we want to have a pretty hard Under-Threshold zone that’s for harder workouts, and a slightly easier distance training zone. We get:
Z1: Easy: HR 120-140
Z2: Distance: HR 140-160
Z3: Under-Threshold: HR 160-170
Z4: Over-Threshold: HR 170-190
Z5: Over-Speed: HR 190-max
Annd, holy crap, we have a sweet 5 zone system!
