# How are Power Zones, (NOT HR zones) computed while running?

I am four weeks into a structured workout. And it’s awesome. When I run slowly, the power graph at the bottom is blue. When I run really fast, it’s red, irrespective of HR. Exactly How is Zwift calculating these color-zones? N.B. I’m not talking HR.
How is Zwift deriving where one zone ends and the next zone begins? Could it be fractions of max speed? How does it get this max speed? And what are the percentages?
I swear, I read the answer somewhere, but I can no longer find it. Sorry to burden you with such a lame question. Thanks in advance

I spoke with ZwiftSupport— they simply do not know how Zwift generates power-color-zones on Zwift Running.

I assume the power-zone choice between green and blue is somewhere between a random number generator and super-secret-proprietary information.

ZwiftSupport also suggests I ask the community forums. Any of you runners know??

Fairly sure it is based on pace rather than power so will be set based upon the times you enter for 5km, 10km etc in your profile.

I think so too. I’m just trying to figure out which pace, or some combination / weighted average of paces.

Long story short, some time ago I created a sham-runner named ChrisGhost (changer65536@gmail.com). He has white hair and white skin, and wears a white shirt.
“He” is running with directly programmed ESP-32 running BLE protocol connected to my macbook pro over a serial cable. “He” is able to run exactly 6.00 MPH, 8.00 MPH or any other speed. “His” original purpose was to serve as a ghost pacer with me-- yes, I run with a robot. But tonight, "he’s going to help me test some paces.

The plan, this evening is to do some testing. He is going to run speed ramps with different 5K, 10K etc paces and I’ll video each test run using QT recorder. I’ll note when the colors change.

You can tell my family is on vacation. I’l running with pretend ghosts and watching colors change.

“He’ll” be on the 5K loop shortly.

Ok. I figured it out. Here is the picture of the ghost’s ramp profile. (Sorry, he changed to pink because he kept getting mauled by zroupies.
You can see he goes through all the colored zones based on speed. Initially, I set all times (in the public profile) based on a 6:00 minute mile. (10 MPH)

Calculating percentages of 10 MPH makes the math easier, later on. As a product of the American Educational system, I don’t do math good.
Next, I ramped again but with the marathon pace set to a 5:00:00 marathon time (slow-- really slow). Nothing Changed. The rainbow colors remained.

Then again with the HM pace set to a 5:00:00 half marathon time. Again, nothing changed.

But… When I changed the 10K pace, to something like 30 minutes per mile the picture changed to this…

AHA! Now, The ghost is in the red zone-- which you would expect if he’s running a ramp with an estimated 10K time of 3 hours.

For the sake of completeness, I finished off by restoring the 10K time and altering 5K and 1Mile times to ridiculous values. And again, nothing changed.

So. Here’s what I got.
Zone color is based exclusively on 10K pace
Gray 0-56% 10K pace
Blue 56-76% 10K pace
Green 76-90%
Yellow 90-100%
Orange 100-106%
Red >106%

These may be totally wrong-- if anybody has better information, let me know. Thanks

5 Likes

For the sake of (even more) completeness, here’s exactly how Zwift computes Heart Rate Zones and Colors.
BLUE (Endurance Zone) 0 - 65% Max HR
GREEN (Fat Burning Zone) 65%+1 - 75% Max HR
YELLOW (Tempo Zone) 75%+1 - 85% Max HR
ORANGE (Threshold Zone) 85%+1 - 95% Max HR
RED (Anaerobic Zone) 95%+1 to infinity Max HR (Actually, the max HR that can be transmitted over BLE is uint8_t 255)

3 Likes