Originally Posted by
cd34
I don't have a power meter currently, so, average speed is what I've been using to judge. However, wind conditions around here are quite variable, so, I don't really know by speed whether it was a good day or not. Was looking at 2x20s three days a week which would allow me to take my longer ride on Saturday.
You don't need a powermeter. If you have a HRM that would be helpful but you can do these on perceived exertion. They don't need to be done at a precise power number, usually a range between 90-100% of your threshold power is good. If you start doing them regularly you will understand how they feel throughout the interval.
If you do them at constant power they should feel hard, but manageable, for the first 5 min. You should be breathing hard but not panting. After 5 min you might start to feel a burning sensation in your legs and it will become more difficult. Keep riding on the edge of that burning sensation. The last 5 min will be harder but the end will be in sight so you should be able to make it. If you're totally gassed at the end of 20 min you probably went too hard and may have trouble on your next interval. Your HR should slowly rise throughout the interval.
A hill with a steady grade that is an excellent substitute for a powermeter. You can use speed on the hill as your guide. If you have a straight flat section without traffic you might be able to use speed to maintain a steady effort but I don't have access to anything that isn't affected by wind or vehicles. Below is an interval from yesterday. Note how the power is relatively constant but the speed varies from about 32 to 42kph. I was doing a loop that took around 12min.
