My pet hate 🙄 is newer runners slowing themselves down too much for the sake of “staying in zone 2”.
Hear me out…
In this rant/blog I’ll cover;
you will still get fit in zone 3
staying in zone 2 often means walking
zone 3 running is fun, and often mechanically nicer
your zones are not accurate anyway
wrist-based HR is useless.
Let’s talk about and define the zones first. We’ll use the classic 5-zone system here.
Zone 1 is basically walking and is not in this chat.
Zone 2 is slow running, often requiring walk breaks to keep the HR in the zone. There are four main positives of training in z2:
main fuel source is fat oxidation (improving this can help endurance performance)
improves peripheral capillarisation and mitochondrial biogenesis (the adaptations that get more oxygen to our working muscles)
has a lower central nervous system tax on our body than faster running.
it’s pretty easy, and you can go for hours.
Zone 3 is a little bit quicker, but still nowhere near “fast” or “threshold” running.
main fuel source shifts towards carbohydrate.
there’s a slight increase in lactate production but the body is able to clear it effectively.
peripheral capillarisation and mitochondrial biogenesis still happens in z3.
this is the zone that most runners feels most mechanically comfortable.
The main theory goes that endurance runners should train primarily in zone 2, for the endurance adaptations it brings. And whilst that’s not entirely wrong, a consequence of constantly aiming for z2 has meant that zone 3 has been demonised 😔 It’s been referred to as the “grey zone” and runs in this zone are just “junk miles”. BUT, as crazy as it may sound, you’ll still get fit if you run in zone 3!
I think the “stick to z2” messaging is beneficial for one specific cohort of runners: the newer runner who blasts every run as fast as they can, and zone 4 running is all they know. Learning to slow down and just “jog” is very important if long distance running is going to be sustainable for you.
But for a lot of newer runners or those who don’t have a highly trained cardiovascular system, you’ll shoot to z3 pretty quick when you run. Religiously sticking to z2 for your easy runs often means you have to stop and walk. That’s not very fun is it. I’d rather my runners drift into zone 3 and actually have a nice run. And still get fit. Crazy, I know.
The obvious caveat here is that we don’t want to fall into the trap of running all our easy runs too fast “because it feels good”. It still needs to feel easy, and importantly, repeatable. If you’re pulling up the next day with soreness or fatigue, we might need to reign you back in.
HR zones are bullshit anyway.
The HR zones that our watches and the internet gives us are purely algorithm-based and ignore our huge individual variability. If you haven’t done a proper VO2 test in a lab, then your HR zones are rubbish and likely wrong.
I used to do VO2 testing at work. (We stopped in 2020 as sharing the mask wasn’t cool in Covid 😷). What I found very interesting was the final number our system pumped out as your Relative VO2 Max was always the same as what your Garmin said. That’s the number like 45 or 56 or whatever yours might be. Measured in mL/kg/min (millilitres of oxygen used per kg of bodyweight per minute). It always agreed with Garmin which I found quite cool.
HOWEVER, the zones were wildly wrong. Each of us has our own zones, even if we are the same age and have the same VO2 Max number. All Garmin (and other companies) can do is estimate our zones until we’ve done a lab VO2 Max test. And the zones are very rough at best.
Imagine you’d spent your whole running career trying to keep your HR under 128 BPM to stay in zone 2 because that’s what your watch said, but your actual zone 2 extends up to 140 BPM.
Wrist-based HR is useless
If you’re going to use HR as a measure in your running, get a chest strap or an upper arm strap. HR measured on watches is notoriously inaccurate and not reliable.
(Interestingly, one reason the watch struggles is when your HR gets close to your cadence, the sensors get confused and overlap. I think that’s so cool!)
Z3 usually feels nicer
We all have a pace where we are mechanically most comfortable and that pace usually feels nice. If you then make a runner artificially slow down because their HRM told them to, they will often run in a heavier, more impactful way. And that usually feels awkward. That’s not how I want my runners to run.
Running should be fun
Maybe this is just me, but a big part of running is actually just feeling good and settling into a rhythm. The thought of jogging along, feeling nice, but then having to drop my pace by 20 sec/km or walk for a bit because I noticed I drifted into z3 suuuucks. You’re gonna get fit if you’re in z3. As long as it still feels easy and sustainable.
So don’t worry too much about z2. Let it inform your runs but not dictate your runs. Be sensible and keep it repeatable.
Rant over.