Hello, I was hoping someone could help me understand the difference in prescribed pacing for an easy/steady run in Z2 versus the predicted VT1 in my running pace profile.
My VT1 (predicted) is currently 8:47 min/mile while the pace range prescribed for a Z2 run is 7:02 - 7:58 min/mile. I’m pretty sure the bottom 1/2-2/3s of that range is outside my Z2 heart rate (based on recent lab data and the talk test).
Looking at the Athletica zones, I think the top of Z2 should be my VT1. Is Athletica using another number (e.g. critical speed) to calculate pace ranges?
Thanks!
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In the 7 zone model, used by Athletica, VT1/MAF sits at the top of zone 2 like you indicated correctly.
Yes, Athletica uses critical pace from a 5km test. Please be mindful of erroneous data from runs used to calculate CP.
When in doubt, if the zone 2 pace is outside of what feels right, then perhaps a test week would help characterize your current fitness level. In the test week is a MAF 8km test and a 5km all out effort. IME, best don’t alone, on flat ground, in a controlled or repeatable environment.
Also, daily fluctuations will occur which is why there are ranges of training zones. Recovery, life stress, hydration, nutrition, what you did yesterday, will impact the ranges. I would say, on any given day, if your HR fluctuations are within plus or minus 5 percent of normal ranges then you are ok.
For example:
My MAF is about 143, it’s an all day cruising pace on flats and nice conditions. If I’m running at the same relative effort, and I notice in the first 10 minutes I’m not feeling great and I can’t keep it out of the 150s, I know I have to cut the workout duration. Conversely, and more tricky is the low hr for a given pace. Often times people think that is always good, but the inability to elevate your HR with pace increases is often a sign of tiredness. Say I try a zone 4 effort, slight pickup, 2 to 3 minutes. If I can’t get my hr into a mid range sub threshold value like sub 160 easily, then I know something is off. I would say, most easy/steady runs, I start off trying to keep my hr below 140 and use RPE to try and disassociate my mind from constant feedback or numbers and just try to enjoy running. I have an issue with just getting lost in data and realize it’s a small part of the entire process.
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Hey,
Thanks @amn2099 for your thoughts 
If I understand correctly, your VT1 pace based on lab tests is much lower than the upper zone 2 pace described by Athletica.
I would not worry too much about the pace. Do your zone 2 work by HR. To keep your aerobic engine purring like a happy kitty, aim at 180-your age/talk test/nose breathing and forget about the pace.
Rule of thumb: hiit work by pace or power and aerobic work by heart rate.
It can be frustrating to have to go slow to keep heart rate in check, but once you start seeing pace pick up, it’s pretty awesome. You’ll feel amazing too and those runs feel like a walk in the park….
Hope this helps
Best, MJ
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Thanks @amn2099 and @Marjaana - super helpful! I did complete a test week last month but now I remember that the MAF test felt off. I was forced to do it on the treadmill due to ice on the roads, which affected pace and HR. Looking back at the data, I think this is why the Z2 pacing is off.
I’ll continue to do Z2 work by HR but I’m curious if I can redo the MAF test without doing the entire test week over again.
Thanks for your help!
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Absolutely!!! 
Go back to your test week, save the MAF test to your library and schedule it from there to your diary.
MJ
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Zone 2 training is hard to get right. IME, the sensations of HIIT are more noticeable. Lots of muscular feedback, breathing is rhythmic. Long duration zone 2 could end up in L3a. Filip talks about that in a video. Maybe MJ can link that here. They talk about what’s better: 30/30s or longer HIIT and touch on long duration VT1 and how someone could end above that marker.
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Indoor running pace on a treadmill can be wildly different due to many factors. With a footpod (calibrated to outdoor GPS), indoor running can be more meaningful, but it’s not the same as outdoor running due to the variation of terrain. You can think of the treadmill controls as intensity control rather than speed.
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Good stuff here and totally agree for Zone 2 work or knowing when you’re crossing VT1 it’s usually best to go by HR and not pace. I also don’t look much at the VT1 metric here since it’s way off in my case (by almost 2 minutes/mile). I assume it gets more accurate as you put in more max efforts over a variety of durations. You can always look at the coach suggestions in your pace profile for what you can do to improve on the accuracy of those metrics too.
LOTS of ways figure out that VT1 line and pace is the least accurate IMHO. The most simple way you already have…your own body. When you approach VT1 you start breathing harder and taking more breaths. If you’re out of breath then slow down or walk. Sometimes it doesn’t have to be any harder to figure out than that. You can add in nose breathing as some find that the point where they can still breathe out of their nose is totally aerobic and when they can’t then you’re approaching or have crossed your VT1. You can also go by perceived effort where an easy zone 2 effort is usually a 2-4 on a exertion scale of 1-10. Finally you can go by percentage of max HR where most seem to cross VT1 around 78-82% of your max. I usually average it out to 80% for most people since the math is easier 
Anyway, the cool thing is usually ALL of those indicators line up nicely and all kind of go off simultaneously as you start to creep past the threshold. The better you get at listening to your body then the easier it gets to keep it all in check.
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So much helpful information here. Thanks, everyone! Completely agree on better ways than pace to identify that VT1 line and when you’re moving past that threshold. My brain wants all the numbers to line up, all the time, but this is a good reminder that’s not always possible
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