This is why I like to train at 4:45am first off - also it is a reason that I like to use power for intervals rather than HR.
If you find out where your lactic threshold is during the am or pm hours that you normally do your workouts...you build your zones based off those numbers. If you did your 20 minute TT to find your thresholds inthe afternoon then used those HR readings to build your zones for morning workouts you could be taking it too easy and vice versa - PE is also very important to use in order to learn your body and how it feels at certain levels and zones - you would benefit for being on a work out regiment that is offered locally by one of the most respected coaches in the world. Graham from www.outsidesport.com
can put together a program that will make you faster and help you go longer. He also has the best line of supplements I have ever used. There are some great deals going on right now for Christmas. Go order from the site now and use promotional code JS and get 10% off the great products they carry and even get an additional 5% off the new promotional Holiday packages.
GO FASTER - GO LONGER