Hi.
Does this need to be done outdoor? I don’t have a power meter on my bike, only on my trainer. Can I do the test on the trainer?
What about the heart rate zones ? I have noticed in the past that my heart rate is significantly higher while riding outside than it is inside. Does it mean I should do a test outside for the heart rate and on the trainer for the power?
Thanks
Hi remy,
I am not a coach and am sure that the great coaches here will respond it quickly 
Here is my perspective :
It’s normal for the power and the HR to be lower indoors than outdoors. Some people have different power/FTP indoor and outdoor, saying that it’s better to train on the same power meter rather that do the test indoor and train outdoor with the same FTP.
But to answer your question - do the 20min test indoor because that’s where you have the power meter. After the 20min test you will know your HR zones also.
Training with power outside will require to do the same test outside. Vice versa.
If i am wrong the coaches can correct me here
There’s this article Fascat has online.
I do mine indoors for a few reasons; repeatability of conditions year-round, hard to dodge traffic every time, and not enough high speed gears for the terrain. I just cannot find a 20 minute (or longer) stretch of road without steep descents, relative to power target, and stop signs.
Hi Remy,
Sounds like you got some good answers here.
First we do recommend that our athletes do their test outdoors. Typically most will produce more power outdoors than compared to indoors. Can see as much as a 5% difference. However without a powermeter to use outdoors doing indoors is fine. It is all you have. You need the power zones for when you are training indoors.
That is interesting that your heart rate is higher outdoors compared to indoors. Again I usually find athletes heart rate higher indoors than outdoors. Well this is unless it is summer when it is hot and humid. That wreaks havoc on heart rate. Heart rate has many variables so it makes it a big trickier to nail down. Power is instant and absolute.
So to answer your question for when you train outdoors you need to use your outdoor heart rate. Threshold heart rate is what you can hold for an hour. So you can even look back on your training and see what your highest 1 hour heart rate average is and compare it to your test. That should get you close.
Also don’t forget to use perceived exertion. Heart rate will take time reflex the effort. So don’t start too hard on them, unless they are full gas of course. 
Watch your heart rate as you are riding indoors with power and get an idea how it reacts and what it is in certain power zones.
I hope that clarifies things. M
That’s fantastic.
Thanks for all the info.