I started my 10 mile round trip per day commute this Spring and during the first 1 to 2 months I could realy feel my legs. The 1st few weeks were not full time since there was still come days of seriously nasty weather. At first it didn't look like I was making much progress. After a while I realized that I was also riding faster and faster each month. I ride on a hybrid bike as I ride in traffic and need to keep my head up and I also have the front shocks since the roads can be pretty bad around here, especially in Spring time. I also carry all my food and drink, fresh shirt, and some emergency repair gear with me. All this means that my setup is not ideal for speed. When I stated riding this spring I considered it a great day when I could average 12 MPH. Now that I've been doing this for about 5 months, my legs don't mind the ride at all and even when I push it hard I have no problems. I can now easily average 16 MPG, and have had days that I was over 18 MPH. Your commute is MUCH longer than mine and your body will definitely take longer to get used to it. Make sure you eat and drink properly before you leave, and keep yourself properly hydrated during and after the ride. I now also frequently get a chance to go to a extra office we just added and then I get an extra 5 mile strech in, and my ride home is lengthed to about 7 miles. I realy like those days now. Start with 2 days a week, then work up to three, etc. It takes some time, but a month from now I'll bet you'll feel it to be much easier.

Happy riding,
André