I had abit of time to play with this now and here is my understanding of it. First here is a sample workout in .zwo format:
<workout_file>
<author>D.Hakansson</author>
<name>BikeToRun</name>
<description></description>
<sportType>run</sportType>
<tags/>
<workout>
<Warmup Duration=“1600” PowerLow=“0.6” PowerHigh=“0.75” pace=“0”/>
<SteadyState Duration=“5000” Power=“0.90” pace=“1”/>
<Cooldown Duration=“1600” PowerLow=“0.7” PowerHigh=“0.25” pace=“0”/>
</workout>
</workout_file>
The main parts here are the three lines inside the <workout>
I have metric choosen and the first part “Duration” is distance in meters. That means that in the choosen file I have 1600m(1mile) as Warmup, 5000m(3,1mi) as main set and another 1600m(1mile) as cooldown.
The next part is twofold the: "PowerLow=“0.6” PowerHigh=“0.75"” means that the workout goes from a 0.6 effort to a 0.75 effort of the choosen pace. Pace is selected lastly on those lines with a number from 0-4 (pace=“0”)
0=Mile pace, 1=5k Pace, 2=10k pace, 3=HM Pace, 4=M Pace
So my workout is simply a Warmup that builds from 60% to 75% of my mile pace during 1600m
After this is the main set a 5k at steady state at 90% of my 5k pace
Finally there´s a cooldown from 70% to 25% of my Mile pace
If I wanted this in a 2x2,5k format instead I would change the <SteadyState Duration> to 2500 and add another line exactly like that one directly below:
<workout>
<Warmup Duration=“1600” PowerLow=“0.6” PowerHigh=“0.75” pace=“0”/>
<SteadyState Duration=“2500” Power=“0.90” pace=“1”/>
<SteadyState Duration=“2500” Power=“0.90” pace=“1”/>
<Cooldown Duration=“1600” PowerLow=“0.7” PowerHigh=“0.25” pace=“0”/>
</workout>
And if I wanted to increase my speed on tht second steady state to 95% of my 5k pace duration I would simply edit like this:
<workout>
<Warmup Duration=“1600” PowerLow=“0.6” PowerHigh=“0.75” pace=“0”/>
<SteadyState Duration=“2500” Power=“0.90” pace=“1”/>
<SteadyState Duration=“2500” Power=“0.95” pace=“1”/>
<Cooldown Duration=“1600” PowerLow=“0.7” PowerHigh=“0.25” pace=“0”/>
</workout>
Hopefully this can help afew build run workouts. Remember though that Zwift needs to be restarted if you edit a workout or else it won´t read the edits you make.
Happy zwifting!